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COLUMBIA    UNIVERSITY 
DEPARTMENT     OF     PHYSIOLOGY 
THE    JOHN    G.   CURTIS    LIBRARY 


SYLLABUS 


A    COURSE    OF    LECTURES 


PHYSIOLOGY 


BY 


J.    BURDON   SANDERSON,   M.D.,    LL.D.,    F.R.S. 

JODRELL   PROFESSOR   OF   PHYSIOLOGY   IN    UNIVERSITY    COLLEGE,    LONDON. 


SECOND  EDITION. 


PHILADELPHIA 

LINDSAY    &    BLAKISTON 
1880. 


PREFACE 


In  the  new  edition  of  the  Syllabus  of  my  Lectures  on 
Physiology,  I  have  followed  the  same  arrangement  as  in 
the  last,  with  the  exception  that  in  the  chemical  part  the 
descriptions  of  immediate  principles,  which  were  before 
printed  separately,  have  now  been  incorporated  in  the 
text.  The  whole  has  been  revised,  and  some  parts  have 
been  much  extended.  Under  the  title  "  Practical  Exer- 
cises," I  have  added  to  the  Syllabus  instructions  for  labo- 
ratory work  relating  to  the  chemical  properties  of  the 
animal  liquids,  and  of  the  most  important  foodstuffs  ;  and 
to  the  physiological  endowments  of  living  tissues  and 
organs.  The  experiments  I  have  selected  are  of  so  simple 
a  character  that,  with  the  directions  given  and  such  aid 
as  he  will  readily  obtain  in  the  laboratory,  every  man  who 
takes  pains  will  find  it  easy  to  carry  them  out  successfully. 
The  chemical  series  already  form  part  of  the  Course  of 
Practical  Physiology.  The  others,  which  relate  chiefly  to 
the  properties  of  the  excitable  and  contractile  tissues,  have 
been  hitherto  omitted  ;  not  because  they  are  regarded  as 
of  less  importance,  but  for  want  of  space — a  difficulty 
which  will  be  removed  as  soon  as  our  new  laboratories  are 
completed.  I  cannot  too  strongly  recommend  their  use 
to  all  who  desire  to  acquire  a  serviceable  knowledge  of 
the  elementary  facts  of  physiology.  They  will  also  fulfil 
another  but  less  important  purpose,  that  of  aiding  candi- 


iv  PREFACE. 

dates  in  their  preparation  for  the  higher  examinations  in 
physiology,  of  the  University. 

To  the  "  Practical  Exercises "  I  have  added  a  series  of 
"  Demonstrations."  Under  this  heading  I  have  given  an 
account  of  experiments  which,  although  they  are  of  such 
fundamental  importance  that  every  student  ought  to  wit- 
ness them,  cannot  be  advantageously  repeated.  These 
are  given  during  the  winter  session,  all  students  who 
have  already  attended  the  summer  practical  course  being 
invited  to  attend  them. 


CONTENTS. 


PART  I. 

PAGE 

The  Chemical  Processes — 

Immediate  Principles  of  Food 2 

Digestion 7 

Intestinal  Absorption i6 

Blood 17 

The  Spleen 22 

Lymph 23 

Chemical  Process  of  Respiration 23 

Urine 26 

Muscular  Tissue 31 

Nervous  Tissue 32 

Exchange  of  Material 33 

Production  of  Heat 41 

Practical  Exercises  relating  to  Food  Stuffs  ...  44 

„                 „                ,,               Animal  Liquids    .        .  48 


PART   II. 

hanical  Processes- 

Muscular  CONTKACTION 

.      55 

Circulation 

.      59 

The  Heart 

.      66 

Respiration 

.      68 

Bodily  Motion 

.      70 

Voice  and  Speech 

.       72 

vi  CONTENTS. 

PART   III. 

PAGE 

Functions  of  Nervous  System — 

Nerves 74 

Functions  of  Nerve  Centres jS 

,,        ,,        Roots  of  Spinal  Nerves        .        .        .        .  8o 

„        ,,       White  Column  of  Spinal  Cord  .        .        .  8i 

Centres  of  Medulla  Oblongata 82 

Death  by  Asphyxia 90 

Reflex  of  Swallowing 91 

Regulation  of  Peristaltic  Action        ....  92 
Influence    of    Nervous    System    on    Processes    of 

Secretion 94 

Regulation  of  Locomotion 97 

,,        ,,          Motions  of  the  Eyeballs    ...  98 

Functions  of  the  Brain 100 

Sensations  and  Perceptions 103 

Tactile  Sensation 104 

Muscular        ,, 105 

Vision  .        .        .        .      " 105 

Hearing      .         .        . 115 

Taste 119 

Smell 121 

Practical    Exercises    relating    to    the    Physiological 
Properties  of  the  Organs  and  Tissues  of  the  Nervous 

AND  Muscular  Systems 123 

Demonstrations 139 


N.B. — Before  using  the  Syllabus  the  Student  must  make  the 
following  corrections  : — 

P.  2,  1.  12  from  bottom,  for  "when  boiled"  read  "at  temperatures  above 
73°  C." 

P.  3,  1.  4,  for  "  bases  "  read  "basis." 

P.  3,  1.  4  from  bottom,  for  ' '  by  the  prolonged  "  read  * '  by  prolonged. " 

P.  9,  1.  22,  for  "dried  gastric  mucous  membrane  and  hydrochloric  acid" 
read  "expressed  juice  of  gastric  mucous  membrane  dried  at  a  low  tem- 
perature. " 

P.  lo,  1.  ^,  for  "bases,  by"  read  "by  basic." 

P.  12,  1.  II  from  bottom,  T^r  "  stercobolin  "  read  "  stercobilin." 

P.  14,  1.  5  from  bottom,  omit  "having." 

P.  15,  1.  \,for  "  Cg"  read  "Cg,"  line  \\,  for  "Hj,,"  read  "Hj." 

P.  12,  1.  2S,for  "solubility"  read  "insolubiHty." 

P.  42,  in  the  table,  for  "9069"  read  "9"o69,"  and  for  "230"  read  "5'230." 

P.  43,  in  the  table, y^r  "at  582  "  read  "X  0-582." 


SYLLABUS  OF  A  COURSE  OF  LECTURES 


ON 


PHYSIOLOGY. 


Part  I. 

THE    CHEMICAL   PROCESSES. 

Animal  life,  as  observed  in  man  and  the  higher  animals, 
is  an  aggregate  of  chemical  processes  for  which  food  and 
oxygen  afford  materials,  the  products  being  heat,  muscular 
action,  carbonic  anhydride,  water  and  ammonia.  Food 
essentially  consists  of  albuminous  bodies,  carbonic  hydrates 
and  fat,  all  of  which  undergo  chemical  disintegration  in 
the  animal  body,  in  addition  to  water  and  certain  inorganic 
salts.  The  fats  and  carbonic  hydrates  are  the  sources 
from  which  the  organism  derives  the  material  for  muscular 
action  and  the  production  of  heat.  Their  carbon  and 
hydrogen  leave  the  body  as  CO^  and  H^O.  Of  the  proteid 
material  used  by  the  body,  a  part  is  represented  in  the 
discharges  by  bodies  of  known  chemical  constitution  con- 
taining nitrogen  (nitrogenous  "metabolites"):  the  remainder 
ev^entually  leaves  the  organism  as  CO.^  and  H^O,  but  may, 
in  the  meantime,  take  part  in  the  production  of  fat,  or  of 
other  non-nitrogenous  immediate  principles. 

Vegetable  life  is  also  a  chemic:d  process.  Green  plants 
build  up  their  tissues  out  of  carbonic  anhydride,  ammonia 
and  certain  inorganic  salts.  Colourless  plants  do  not  dis- 
sociate carbonic  anhydride,  but  derive  their  carbon  entirely 
from  the  soil  on  which  they  grow.     The  most  important 

B 


2  IMMEDIATE   PRINCIPLES 

constituents  of  the  tissues  of  plants  are  albuminous  bodies, 
and  carbonic  hydrates;  for  these  exist  in  all  plants.  The 
characteristic  property  of  a  plant  is  its  power  of  forming 
its  tissues  out  of  inorganic  materials. 

The  term  protoplasm  is  used  to  denote  the  apparently, 
but  not  really,  homogeneous  substance  which  forms  the 
active  parts  of  the  tissues  of  plants  and  animals.  It  con- 
sists chiefly  of  albuminous  bodies,  and  exhibits  in  itself  all 
the  essential  phenomena  of  life :  for  in  it,  not  only  the 
general  actions  which  belong  to  the  organism  as  a  whole, 
but  the  specific  actions  of  particular  parts,  such  as  those  of 
muscle,  nerve  and  gland,  have  their  seat. 

IMMEDIATE    PRINCIPLES   OF  FOOD. 

'"^^  Tlic  ii:r)}i  ''''  immediate  principle'^  or  ^^  proximate  principle''''  {a-Toi^^eiiiii)  is 
applied  to  any  ^^  substance"  in  the  chemical  sense,  which  exists  as  snc/i  in 
livin;^  organisms.  It  is  tinderstood  to  be  applicable  to  bodies  which  are  met  tenth 
in  the  secreted  liquids,  as  toell  as  to  the  constituents  of  the  blood  and  tissues, 

AlhujMIXOUs  Bodip:s  (Proteids). 

Proteids  are  non-ciystallizal:)]e  bodies  of  unknown  constitution,  of  which 
the  centesimal  composition  is  about  Carbon  53,  Hydrogen  7 "5,  Nitrogen 
1 5 '5,  Oxygen  23,  Sulphur  i 'o.  They  are  soluble,  or  capable  of  imbibition 
with  water,  insoluble  in  alcohol  or  ether.  They  are  all  stained  yellow  by 
nitric  acid,  and  then  disintegrated,  leaving  a  yellow  precipitate  which  dissolves 
orange  red  in  ammonia. 

Aqueous  solutions  of  proteids  are  iKvo-rotatory.     When  a  solution  is  sepa- 
rated from  water  by  a  septum  of  colloid  membrane,  the  proteid  diffuses  with 
A  extreme  slowness  into  tlie  Mater. 
ojfyjL/x'^  '      They  occur  in  the  tissues  or  fluids  of  plants  and  animals  under  two  prin- 
/  --,  cipal  forms,  distinguished  from  each  other  according  as  they  are  coagulated  or 
^  remain  in  solution  (J^iSSSSiSfit  ' 

Z^m  ^  T^^  coagulable  ])roteids  coitijSrise  the  albumins  proper,  which  are  soluble  in 

water,  and  the  glol)ulins,  which  are  insoluble,  but  are  readily  held  in  solution 

'  in  presence  of    neutral  salts,   particularly  NaCl.     From  these  (often  called 

native  albumins)   the  mass  of  the  proteid  material  of  animal   and  vegetable 

tissues  is  formed. 

The  albuminates  are  soluble  in  aqueous  liquids,  only  when  these  are  acid 
or  alkaline  :  they  are  precipitated  by  neutralization.  They  must  be  regarded 
as  derivates  from  the  others ;  for  bodies  which  correspond  entirely  in  their 
characters  with  those  albuminates  which  exist  in  the  tissues  of  plants  and 
animals  can  be  obtained  by  the  prolonged  action  of  alkalies  or  acids  on 
coagulable  proteids. 


OF   FOOD.  3 

AlbuinhioUs. — There  exist  in  the  animal  body  several  substances  which, 
although  close  allied  to  the  proteids,  are  separated  from  them  by  several  well- 
marked  dilTorences.  One  of  these,  Colla^c-n,  is  of  great  importance,  as  yield- 
ing 6't7<z//V/.  It  constitutes  the  "organic  bas^s  "  of  bone,  and  is  the  most  1/ 
important  constituent  of  the  connective  tissues  generally.  Gelatin  is  the  pro- 
duct of  boiling  "  collagen."  It  swells  in  cold  water,  but  does  not  dissolve  ; 
its  solution  in  hot  water  "gelatinizes"  on  cooling.  It  is  precipitated  by 
tannin  and  corrosive  sublimate,  not  by  acetic  acid  and  potassic  ferrocyanide. 
ChoiiJn'ii,  a  similar  protluct  obtained  from  cartilage,  is  distinguished  from 
gelatin  liy  being  precipitated  by  acetic  acid. 


Carbohydrates, 

Cdlulosc. — The  material  of  the  outer  membrane  of  the  plant-cell  is  un- 
affected by  dilute  acids  or  alkalies,  but  is  converted  by  strong  sulphuric  acid 
into  a  body  which  is  coloured  blue  by  iodine. 

Starch  is  the  chief  constituent  of  the  "  Starch  grains  "  contained  in  the  cells 
of  plants  ;  in  these  grains  it  is  enclosed  in  concentric  envelopes  of  an  insoluble 
bcKly  resembling  cellulose  ;  it  is  soluble  in  water,  the  solution  being  opalescent ; 
it  is  coloured  blue  by  iodine ;  the  blue  colour  disappears  on  heating,  but  re- 
appears on  cooling,  unless  the  heating  has  been  long  continued.  Starch  is 
converted  by  prolonged  action  of  weak  acids  into  Dextrin  (a  body  which  is 
coloured  red  by  iodine),  and  eventually  into  grape  sugar.  It  is  converted  in 
presence  of  diastatic  ferments,  c.^.,  those  of  the  salivary  glands,  pancreas,  and 
liver  into  grape  sugar. 

Grape  Sugar  or  Dextrose  or  Starch  Sugar  (Cg  II,j  Og)  occurs  in  extremely 
small  quantity  in  blood,  muscle,  and  other  tissues,  and  (according  to  Briicke) 
in  normal  urine.  It  is  distinguished  by  its  power  of  reducing  certain  metallic 
salts,  by  its  dextro-rotatory  action,  by  its  splitting,  when  subjected  to  the 
action  of  the  yeast-plant  at  a  suitable  temperature,  into  alcohol  and  carbonic 
acid,  and  by  its  yielding  lactic  acid  in  presence  of  albuminous  bodies  in  process 
of  putrefaction.  It  is  soluble  in  li  parts  of  cold  water,  and  to  any  extent  in 
boiling  water.  From  its  solution  in  boiling  alcohol,  it  readily  crj'stallizes. 
On  the  power  of  reduction  possessed  by  grape  sugar  depentls  the  important 
test  known  as  "  Trommer's  Test,"  which  consists  in  adding  solution  of 
potassic  hydrate  to  the  liquid  supposed  to  contain  sugar,  and  then  weak 
solution  of  cupric  sulphate,  so  long  as  the  precipitate  of  cupric  hydrate  first 
formed  redissolves  on  agitation.  On  gently  heating,  a  yellow  precipitate  is 
formed  of  cuprous  hydrate,  or  a  deposit  of  cuprous  oxide  {see  Practical  Part, 
Section  II.) 

Milk  Sugar  or  Lactose  constitutes  about  15  percent,  of  the  solids  of  milk  : 
it  can  be  obtained  directly  from  whey,  after  separation  of  albuminous  com- 
pounds, by  crystallization  in  rhombic  prisms  (C,,  Hjj  O,,  •\-  IIj  O)  :  it  is  con- 
verted by  '^^j^  prolonged  boiling  with  weak  acids  into  fermentescible  sugars 
(galactose  and  dextrose) ;  it  is  transformed  very  readily  into  lactic  acids 
under  the  influence  of  a  ferment  usually  present  in  milk. 

Cane  Sugar  does  not  occur  in  the  animal  body,  but  is  an  important  con- 

B    2 


4  IMMEDIATE   TRTNCIPLES 

stituent  of  food.     When  Ijoiled  with  dilute  acids,  cane  sugar  is  converted  into 
dextrose  and  levulose.     A  similar  change  takes  place  in  gastric  digestion. 

Fats. 

Palmitm  (C,  K,  (C.e  H^,  0)3  O.)  and  SLm-m  (C,  H,  (C.^  PI35  O)^  O3), 
which  in  solution  in  olein  constitute  animal  fat,  are  insoluble  in  water,  soluble 
in  hot  alcohol,  ether,  chloroform,  benzole,  &c.  Under  the  influence  of  super- 
heated steam  they  are  decomposed,  taking  up  water  and  yielding  glycerine 
and  Palmitic  and  Stearic  acids  respectively.  (C3  H5  (Cia  H3,  0)3  O3  +  3  HjO 
=  C3  Hj  (Hg)  O3  +  3  Cjg  H32  Oj.)  A  similar  change  takes  place  more 
gradually  under  the  influence  of  pancreatic  secretion  in  the  intestine,  as  well 
as  in  presence  of  albuminous  bodies  in  putrefaction.  Alkaline  palmitates  and 
stearates  (Soaps)  are  obtained  when  fat  is  dissolved  in  potash  or  soda  with  the 
aid  of  heat ;  such  soaps  exist  in  bile.  When  fat  becomes  rancid,  it  not  only 
undergoes  transformation  into  acids  and  glycerine,  but  takes  up  oxygen,  in 
consequence  of  which  volatile  and  pungent  acids  belonging  to  the  same  series 
(Cji  Hon  O2),  but  containing  less  carbon,  are  formed. 

Palmitin  fuses  at  40°  C,  Stearine  at  about  60°  C.  According  to  the  pro- 
portion in  which  they  exist  in  different  kinds  of  fat,  the  fusing  points  of  such 
fats  vary.  Thus,  while  beef  fat  fuses  at  37°  C,  and  contains  three  parts  of 
Stearin  and  Palmitin  to  one  part  of  olein,  human  fat,  which  contains  less 
Stearin  and  relatively  more  olein,  fuses  at  25°  C.  O/ctn  (Cg  H.,  (C|8  H33  0)3 
O3),  is  the  fluid  fat  in  which  stearin  and  palmitin  are  dissolved.  Olein  solidifies 
a  few  degrees  above  freezing  point,  and  is  more  soluble  than  the  other  fats  in 
ether.  Palmitic  Acid  (C|g  H;;2  Oj)  and  Stearic  Acid  (Cig  H33  Og)  are  crystalline 
bodies,  chiefly  distinguished  from  each  other  by  their  relation  to  heat,  the 
former  fusing  at  62°  C,  the  latter  at  70°  C.  Their  relations  to  solvents  cor- 
respond with  those  of  the  fats.  Palmitic  acid  crystallizes  from  its  solution  in 
hot  alcohol  in  bunches  of  fine  needles  ;  stearin  in  shining  plates.  Oleic  Acid 
(C,g  II34  O2),  which  belongs  to  the  series  Cu  H^n  _  2  O2,  fluid  at  ordinary 
temperatures,  is  decomposed  by  strong  potash,  potassic  palmitate  and  acetate 
being  produced. 

Biityrine  (C3  II;  (C4  H7  O)  O3)  and  the  corresponding  glycerides  of  other 
volatile  acids  (capronic,  caprylic,  and  myristinic)  occur  in  small  proportion  in 
butter. 

Food. 

Flesh  ovjcs  Its  nutritive  value  to  its  albuminous  and  colla- 
genous constituents,  its  fat  and  its  salts.  Lean  meat  (beef) 
contains  about  25  per  cent,  of  solids,  of  which  18  percent, 
is  albumin,  and  yields  about  2  per  cent,  of  gelatin  to 
boiling  water.  Flesh  of  young  animals  (veal)  yields  5  to 
10  per  cent.  The  interstitial  fat  of  meat  varies  in  quantity 
from  4  to  1 5  per  cent. 


OF    FOOD.  5 

Meat  yields  to  warm  water  at  60''  C.  about  3  per  cent,  of 
albuminous  material  and  nearly  as  much  extractive.  On 
boilin^^  the  aqueous  extract,  the  albumin  coagulates  (as 
scum),  but  when  the  boiling  is  long  continued  some  of  it 
redissolves  (Mulder).  Consequently  the  quantity  of  albu- 
minous material  contained  in  bouillon,  always  small,  varies 
according  to  the  mode  of  preparation.  It  maybe  increased 
by  the  addition  of  a  trace  of  hydrochloric  acid  to  the 
water  used.  Bouillon,  beef  tea,  and  other  similar  products 
owe  their  value,  partly  to  the  gelatin,  but  chiefly  to  the  salts 
and  extractive  which  they  contain.  "  Liebig's  Extract " 
contains  neither  proteid  nor  gelatin. 

Meat,  when  roasted,  retains  its  juice,  which,  from  the 
comparatively  low  temperature  of  the  internal  parts  (indi- 
cated by  the  colour)  does  not  coagulate.  The  tenderne;-s 
which  meat  acquires  by  keeping  is  due  to  conversion  of 
some  of  its  myosin  into  albuminate.  Cooking  is  useful, 
not  only  as  preparatory  to  digestion,  but  as  destructive  of 
parasites  and  of  morbid  and  septic  products. 

j\Iilk. — All  of  the  constituents  of  milk  are  of  nutritive 
value.  Cream  consists  chiefly  of  casein  and  butter;  Biiticr 
contains,  in  addition  to  the  ordinary  fats  (Palmitin,  Stearin, 
and  Olein),  about  2  per  cent,  of  the  glycerides  of  the 
volatile  acids;  Eiittcr  milk  consists  of  sugar,  casein  and 
salts;  Whey  of  sugar  and  salts;  Cheese  of  casein  with 
variable  quantities  of  butter,  and  of  the  products  of  de- 
composition of  both.  Human  milk  contains  less  than  4  per 
cent,  of  casein,  between  3  and  4  per  cent,  of  butter,  and 
from  4  to  5  per  cent,  of  sugar.  In  Colostrum  the  casein  is 
partly  replaced  by  serum  albumin.  Cows'  milk  contains 
much  more  casein  than  human  milk,  but  no  more  sugar: 
consequently,  when  the  former  is  diluted,  as  a  substitute  for 
the  latter,  milk  sugar  (which  as  crystallized  from  whey 
always  contains  calcic  and  potassic  phosphates)  must  be 
added.  Cows'  milk  always  contains  a  small  percentage  of 
albumin. 


6  FOOD   STUFFS. 

Eggs. — Eggs  contain  about  73  per  cent,  of  water,  15  of 
albumin,  and  12  of  fat.  Yolk  of  egg  yields  lecithin  {see 
"  Nervous  Tissue  ")  in  considerable  quantity,  and  vitellin, 
a  proteid  body  analogous  to  paraglobulin  {see  "Blood"). 

Vitellin  is  obtained  when  yolk  of  egg,  A\-hich  has  been  previously  extracted 
with  ether,  is  treated  with  solution  of  common  salt.  It  is  precipitated  on  the 
addition  of  water. 

Cereals,  Pulses  and  other  Vegetable  Foods. —  Wheat  floitr 
derives  its  alimentary  value  from  its  large  percentage  of 
proteids  (13  per  cent.)  and  starch  (73  per  cent.),  but  chiefly 
from  its  containing  gluten,  and  its  consequent  adaptedness 
for  bread-making.  In  the  fermentation  of  dough,  grape- 
sugar  splits  into  alcohol  and  carbonic  acid  under  the 
influence  of  the  yeast-plant.  By  this  means  the  dough  is 
raised.  In  baking,  the  dough  is  subjected  to  a  very  high 
temperature  (150"  C.  to  200°  C).  Most  of  the  starch  becomes 
soluble,  and  much  of  it  is  converted,  especially  in  the  crust, 
into  dextrin.  Notwithstanding  the  destruction  of  sugar 
in  fermentation,  a  loaf  weighs  about  a  quarter  more  than 
the  flour  used  to  make  it.  Rye  flour,  nearly  as  rich  in 
proteids  and  starch  as  wheat,  is  also  used  for  bread-making, 
but  yields  a  less  perfect  product.  It  contains  more  cellu- 
lose and  less  albuminous  substances.  Barley  and  Oatmeal 
cannot  be  so  used,  as  they  yield  no  gluten.  They  also 
contain  less  proteids  (5  to  10  per  cent.)  Barley  owes  its 
importance  to  its  being  a  source  of  diastase  and  grape- 
sugar.  Maize,  although  poor  in  albuminous  bodies,  is  rich 
in  starch,  but  in  both  these  respects  it  is  exceeded  by  rice. 
Rye  and  maize  are  severally  liable  to  a  parasitic  disease 
which  renders  the  grain  morbific.  The  Pulses  owe  their 
value  to  the  legumin  they  contain,  and  to  their  large  per- 
centage of  proteid  (23  to  25  per  cent.)  Potato  contains 
75  per  cent,  of  water.  In  the  dry  state  it  contains  about 
8  per  cent,  of  proteid  and  70  per  cent,  of  starch.  Its 
cellulose  becomes  gelatinous  by  boiling,  and  is  thus  soluble 


DIGESTION.  7 

in  the  digestive  liquids.  Fruits  and  siiccnknt  vegetables 
owe  their  nutritive  value  to  the  sugar  and  to  the  organic 
acids  and  the  salts  which  they  contain.  Their  percentage 
of  albuminous  material  is  very  small. 

Inorganic  Salts  of  Food. — Beef  yields,  when  dry,  about 
4  per  cent,  of  ash,  potash  constituting  more  than  two-thirds 
of  the  total  bases.  The  most  important  potassium  salts  are 
phosphate  and  chloride.  The  proportion  of  sodium  salts 
is  very  small.  In  boiling  meat,  nearly  the  whole  of  its 
alkaline  salts  pass  into  the  bouillon.  Wheat  flour  contains 
about  2  per  cent,  of  ash,  of  which  one-third  is  reckoned  as 
potash  and  nearly  half  as  phosphoric  anhydride.  The 
constitution  of  the  ash  of  potatoes  and  other  juicy  vege- 
tables is  similar,  but  the  yield  of  phosphoric  acid  is  relatively 
less ;  the  percentage  of  potash  is  about  four  times  as  great 
as  that  of  all  the  other  bases  together.  Milk  yields  about 
2*5  per  thousand  of  ash,  of  which  about  i  per  thousand 
is  reckoned  as  potash,  0"25  as  soda,  and  about  0*4  as  lime. 

In  an  adequate  diet  comprising  250  grammes  of  meat, 
and  400  grammes  of  bread,  the  former  would  yield  i"5 
gramme  of  potash,  the  latter  v6.  An  adequate  diet  of 
milk  (two  and  a  half  litres)  would  yield  about  3  grammes. 

DIGESTION, 

indndiiig  tlic  Physiology  of  the  Liver  and  Pancreas. 

Human  saliva,  the  mixed  secretion  of  the  submaxillary, 
parotid,  and  sublingual  glands,  and  of  the  mucous  glands 
of  the  mouth,  is  a  tenacious,  slightly  turbid,  and  slightly 
alkaline  liquid  ;  it  contains  about  half  per  cent,  of  solids, 
of  which  about  half  is  inorganic.  The  organic  constituents 
are  albumin,  globulin,  mucin,  and  a  diastatic  ferment ;  the 
salts  are  those  of  the  blood,  but  the  proportion  of  earthy 
bases  is  larger.  Ferric  salts  colour  saliva  blood-red :  this 
reaction  is  due  to  sulphocyanate  of  potassium,  which  it 


8  DIGESTION 

derives  from  the  parotid.  Its  mucin  is  derived  from  the 
submaxillary,  and  its  ferment  chiefly  from  the  same 
source.  Its  turbidity  is  due  to  salivary  corpuscles,  and 
epithelial  elements.  The  salivary  secretion  of  the  dog 
(submaxillary)  contains  no  ferment,  and  no  sulphocyanate. 
It  yields  a  very  large  proportion  of  CO^  to  the  mercurial 
vacuum. 

Saliva  owes  its  value  in  digestion  chiefly  to  its  diastatic 
ferment,  but  it  is  also  of  use  as  a  solvent  and  lubricant. 

Digestion  in  the  Stomach. 

The  relative  importance  of  gastric  as  compared  with 
salivary  digestion  varies  in  different  classes  of  animals 
according  to  the  nature  of  their  food.  In  the  carnivora 
the  food  enters  the  stomach  unchanged,  and  remains  there 
for  many  hours.  The  stomach  is  of  relatively  large  size, 
and  its  whole  surface  is  provided  with  peptic  glands.  In 
the  herbivora,  as,  e.g.,  in  the  horse,  the  thoroughly  masti- 
cated and  insalivated  food  is  retained  only  for  a  very  short 
time  in  the  stomach.  The  organ  is  accordingly  very 
small,  and  only  a  part  of  its  mucous  lining  is  digestive. 

Human  gastric  juice  is  a  colourless  transparent  liquid 
of  very  low  specific  gravity  (1005).  It  contains  neither 
albumin  nor  mucin,  and  may  be  regarded  as  a  solution  of 
pepsin,  hydrochloric  acid,  chloride  of  sodium,  and  other 
salts.  It  is  secreted  by  the  peptic  cells  of  the  glands  of 
which  the  digestive  part  of  the  mucous  membrane  chiefly 
consists.  The  secretion  takes  place  in  answer  to  mechan- 
ical or  chemical  stimulation  of  the  mucous  surface ;  the 
act  is  attended  with  increased  circulation  of  blood  in  the 
mucous  membrane. 

The  process  of  gastric  digestion  consists  in  the  trans- 
formation of  the  albuminous  bodies  of  the  food  into  acid- 
albumin  and  peptone  (parapcptonc),  under  the  combined 
influence  of  pepsin  and  of  a  free  acid.     In  the  dog,  the 


IN    THK   STOMACH.  9 

gastric  juice -^an  be  proved  to  contain  free  hydrochloric 
acid,  for  the  quantity  of  chlorine  in  it  is  considerably  more 
than  sufficient  to  combine  with  all  the  metals  present. 
As  regards  human  gastric  juice  the  proof  is  less  complete. 
Lactic  acid  is  present  in  chyme  whenever  carbohydrates 
are  being  digested.  It  has  been  found  that  hydrochloric 
acid  can  be  replaced  by  phosphoric  acid,  as  well  as  by 
acetic  and  other  acids  of  the  same  series. 

Pepsin,  although  resembling  the  albuminous  bodies  in 
chemical  composition,  exhibits  none  of  their  distinctive 
characters.  It  exists  in  gastric  juice  in  a  state  of  imperfect 
solution,  so  that  it  can  be  removed  from  it  by  mechanical 
means  ;  on  this  fact  Brlicke's  method  of  preparing  pure 
pepsin  is  founded.  It  is  capable  cf  taking  part  in  the 
digestion  of  albuminous  substances,  even  in  the  smallest 
quantity,  provided  that  the  liquid  is  not  too  dilute,  and 
that  it  does  not  contain  too  large  a  proportion  of  the 
product  of  digestion — peptone.  In  the  process,  the  pep- 
sin neither  increases,  diminishes,  nor  undergoes  any  loss  of 
activity. 

The  substance  commercially  known  as  pepsin  consists 
of  dried  gasttJe-muLOus  membrane,  and  hydrochloric  a-etd-. 
A  solution  of  pepsin  which  possesses  its  digestive  proper- 
ties is  obtained  by  extracting  fresh  mucous  membrane 
with  glycerine. 

In  animals  that  die  during  digestion,  the  stomach 
digests  itself  after  death.  During  life  such  digestion  is 
prevented  by  the  alkalinity  of  the  tissues.  Chyme,  as 
it  leaves  the  stomach,  contains  remains  of  animal  and 
vegetable  structure,  unaltered  starch  grains,  fat  particles, 
and  (after  milk  diet)  curd  particles.  It  does  not  normally 
contain  bile.  It  yields  a  mixture  of  gases  in  which  there 
is  much  less  oxygen  than  in  common  air,  and  a  larger 
proportion  of  CO^. 

Peptone  difl'ers  from  pioteids  in  the  readiness  with  which  it  difluses 
through   animal    membranes.     It  resembles   them   in   chemical   composition 


(U^- 


lO  SECRETION    OF   BILE. 

(approximo.te  composition  of  gastric  peptone  in  lOO  parts— Carbon  49, 
Hydrogen  7,  Nitrogen  15,  Oxygen  28,  Sulphur  i).  It  is  soluble  in  water  in 
all  proportions  ;  insoluble  in  alcohol  or  ether.  Its  solution  diffuses  readily  : 
it  is  unaffected  by  heat ;  and,  when  acidulated  with  acetic  acid,  is  not  pre- 
cipitated by  ferrocyanide  of  potassium.  It  is  precipitated  by  tannin  baoos,  by 
C  lead  acetate,  and  by  solution  of  Hg  lo  in  iodide  of  potassium. 

Secretion  of  Bile. 

Human  bile  contains  10  per  cent,  of  solids,  of  which 
about  4  per  cent,  is  bilin,  ly^,  per  cent,  fat,  2  per  cent, 
mucus  and  colouring  matter,  i  to  2  per  cent,  alkaline 
soaps,  I  per  cent,  salts.  It  is  believed  that  about  two 
pounds  of  bile  are  secreted  daily.  The  density  of  bile 
differs  according  to  the  mode  of  collection  and  the  time 
of  secretion.  Bilin  and  fat  originate,  along  with  other 
bodies,  from  proteid  in  the  living  substance  of  the  liver 
cells.  The  colouring  matter  is  derived  from  that  of  the 
blood.  The  mucin  is  secreted  by  the  mucous  membrane 
of  the  gall  bladder.  In  the  intestines  the  bilin  is  decom- 
posed under  the  influence  of  septic  ferment  organisms : 
glycin  and  taurin  are  absorbed,  and  either  return  to  their 
source,  or  may  take  part  in  the  production  of  such  bodies 
as  hippuric  acid,  and  tauro-carbamic  acid,  which  appear  in 
the  urine  ;  cholalic  acid  is  in  great  part  lost  in  the  faeces. 
The  fats  and  soaps  are  absorbed.  The  colouring  matter  is 
transformed  by  reduction  into  a  body  having  the  char- 
acters of  hydrobilirubin. 

In  intestinal  digestion  the  bile  is  antiseptic,  and  there 
is  reason  to  believe  that  it  also  promotes  the  absorption 
of  fat. 

Nothing  is  as  yet  known  as  to  the  influence  of  the 
nervous  system  on  the  secretion  of  bile. 

BiLIX. 

Bilin  (or  Bile  ciysials),  as  obtained  from  ox  bile,  consists  chiefly  of  sodic 
glycocholate  (Cjg  H4J  Na  NO^),  with  a  much  smaller  proportion  of  tauro- 
cholate  (Cjo  ll^^  Na  NO7  .S).  Bilin  of  dogs'  bile  consists  exclusively  of 
taurocholate.     These  soap-like  bodies  ciystallize  from  the  alcoholic  solution 


h 


BILIN.  1 1 

of  the  dry  residue^f  ox  bile  on  the  adilition  of  ether.  The  crystals  are  very 
soluble  in  water  and  have  the  peculiar  bitter  sweetness  of  bile.  The  solution 
is  dextrorotatory.  With  concentrated  sulphuric  acid  it  becomes  resinous  and 
yields  after  a  time  a  yellow  liquid  having  a  green  fluorescence.  If,  after 
adding  a  trace  of  cane-sugar,  a  liquid  containing  bilin  is  mixed  with  sulpliuric 
acid  and  kept  at  a  temperature  between  50°  C.  and  600  C,  a  purplish  violet 
solution  is  obtained,  which  shows  before  the  spectroscope  an  aljsorption  band 
at  E  and  another  near  F,  Solution  of  ox-bile  crystals  is  precipitated  by  the 
addition  of  neutral  acetate  of  lead.  The  heavy  precipitate  consists  of  lead 
glycocholate.  By  treating  its  solution  in  hot  alcohol  with  sulphuretted 
hydrogen,  fdtering  and  adding  water  to  the  filtrate,  glycocholic  acid  (Cjg  1143 
NOa)  is  obtained  as  a  resinous  precipitate.  Glycocholic  acid  is  sparingly 
soluble  in  water,  readily  in  hot  alcohol,  from  which  it  crystallizes.  When  it 
is  boiled  with  strong  hydrochloric  acid  it  is  converted  into  a  soluble  com- 
pound of  hydrochloric  acid  and  glycocoll,  which  is  very  soluble  in  water,  and 
a  resinous  product,  often  called  hilc-rcsiti,  consisting  of  cholalic  acid  and 
dyslysin  {sec  Cholalic  Acid).  When  the  liquid  from  which  the  lead  glyco- 
cholate has  been  precipitated  is  treated  with  basic  lead  acetate,  with  the 
addition  of  ammonia,  a  second  precipitate  is  obtained  of  lead  taurocholate. 
By  suspending  the  lead  precipitate  of  dogs'  bile  in  alcohol,  decomposing  it 
with  HjS,  filtering,  concentrating  the  filtrate,  taurocholic  acid  (C25  H^.-  NO7S) 
is  obtained  in  solution.  On  the  addition  of  ether  a  syrupy  precipitate  is 
formed,  which  afterwards  crystallizes.  It  differs  from  glycocholic  acid  in  being 
excessively  soluble  in  water,  and  splitting  much  more  readily  into  cholalic 
acid  and  taurin,  than  glycocholic  acid  does  into  cholalic  acid  and  glycocoll. 

Glycocoll,  Glycin  or  Gelatin-sugar  (Cj  II5  NOj  or  (as  Amido-acctic  acid)  Cj 
H3  (NII2)  O^,)  is  obtained  from  glycocholic  acid  by  prolonged  boiling  with 
strong  hydrochloric  acid.  The  firm  resin  ^\■hich  is  formed  consists  of  cholalic 
acid  and  dyslysin  {see  Cholalic  Acid);  this  having  been  separated,  the 
remaining  liquid  yields  on  evaporation  glycocoll-hydrochlorate  (Cj  H^  NO^,  H 
CI).  From  the  aqueous  solution  of  this  substance  glycocoll  is  obtained  by 
treating  it  with  hydrate  of  lead  oxide  and  then  decomposing  the  soluble  lead 
glycocoll,  after  sej>arating  the  chloride,  with  sulphuretted  hydrogen.  Glyco- 
coll is  soluble  in  five  parts  of  cold  water,  and  insoluble  in  absolute  alcohol 
and  ether.  It  crystallizes  from  hot  dilute  alcohol  in  hard  rhombohedral 
crystals.  Its  solution  in  water  has  an  acid  reaction  and  sweetish  taste. 
It  is  called  "gelatin-sugar"  because,  along  with  the  body  Leucin,  it  is  a 
product  which  is  obtained  when  gelatin  is  acted  on  by  sulphuric  acid.  Glyco- 
coll has  been  obtained  synthetically  by  the  action  of  monochloracetic  acid  on 
ammonia.     (Cg  H3  CI  O,  +  NIl3=  IICl  -f  Cj  H3  (NHj)  Oj.) 

Tainin  (Cj  H,  NSO3)  is  best  obtained  from  the  bile  of  the  dog,  in  which 
the  whole  of  the  bilin  consists  of  taurocholate.  By  boiling  bilin  with  hydro- 
chloric acid,  separating  the  resin  and  evaporating  the  acid  liquid,  a  residue 
is  obtained  from  which  (after  the  glycocoll-hydrochlorate  has  been  removed 
by  extracting  it  with  absolute  alcohol),  taurin  can  be  procured  by  treating  it 
with  boiling  water.  Taurin  is  soluble  in  fifteen  parts  of  cold,  and  very  soluble 
in  hot  water,  sparingly  in  cold  alcohol.  It  crystallizes  very  readily  in  large 
4-  or  6-sided  shining  prisms,  each  of  which  ends  in  a  4-sided  pyramid.     The 


12  BILIN. 

constitution  of  taurin  can  be  best  understood  by  remembering  how  it  is 
obtained  synthetically,  viz.,  by  subjecting  amnionic  isethionate  (NH^,  C2  II5, 
S0^)  to  a  high  temperature,  in  consequence  of  which  it  loses  the  elements  of 
a  molecule  of  water.  Neither  the  origin  nor  the  destiny  of  Taurin  in  the 
organism  is  known.  It  was,  until  lately,  supposed  that  it  was  represented 
in  the  urine  by  sulphates,  and  that  its  amide  took  part  in  the  constitution  of 
urea  ;  but  it  has  been  recently  proved  experimentally  that  when  dogs  are 
fed  with  Taurin,  that  body  leaves  the  organism  partly  as  such,  but  chiefly  in 
the  form  of  Tauro-carbamic  acid  (C3  Hg  Nj  Oj). 

Cholalic  Acid  (C24  H^g  O3)  is  insoluble  in  water,  veiy  soluble  in  alcohol, 
sparingly  in  ether.  It  ciystallizes  from  its  solution  in  dilute  alcohol,  in 
tetrahedra  or  octahedra,  which,  at  first  transparent,  soon  become  opaque  on 
exposure.  At  high  temperatures,  it  loses  HjO  and  yields  dyslysin  (Cj,  H^e 
O3)  and  undergoes  a  similar  change  when  boiled  with  hydi-ochloric  acid.  It 
is  contained  in  decomposed  bile  as  alkaline  cholalate,  and  is  precipitated 
therefrom  on  the  addition  of  acetic  acid.  From  this  precipitate  it  can  be 
extracted  by  alcohol. 

Bilirubin  (Cholepyrrhin  C35  H3Q  N4  Og)  can  be  obtained  directly  from  human 
bile,  or  from  that  of  the  dog  by  shaking  it  with  chloroform.  On  separating 
the  solution  thus  obtained  from  the  bile  and  then  distilling  off  the  chloroform, 
a  pitchy  residue  is  left,  which,  after  it  has  been  exhausted  by  alcohol,  is  found 
to  contain  crj-stals  of  bilirubin.  The  alcohol  contains  cholesterin  and  a  brown 
colouring  matter  which  has  been  called  bilifuscin.  Bilirubin  is  a  principal 
constituent  of  biliaiy  calculi ;  pow'dered  gall  stone  is  first  extracted  with  ether 
to  remove  the  cholesterin,  and  then  treated  wdth  dilute  hydrochloric  acid  and 
washed  :  the  residue  yields,  when  treated  with  chloroform,  a  yellowish-brown 
solution,  from  which  bilirubin  is  precipitated  on  the  addition  of  alcohol,  or 
crystallizes  on  evaporation,  in  red  needles.  It  is  insoluble  in  water,  nearly 
insoluble  in  boiling  alcohol  and  in  ether,  more  soluble  in  bisulphuret  of  carbon, 
and  most  of  all  in  chloroform.  Its  solution  shows  no  absorption  bands.  It 
further  dissolves  I'eadily  in  potash  or  soda,  and  when  the  alkaline  solution  is 
exposed  to  air,  it  gradually  becomes  green,  and  gives,  when  treated  with 
hydrochloric  acid,  a  green  precipitate  [biliverdiii),  which  is  insoluble  in  chloro- 
form but  soluble  in  alcohol.  Bilirubin,  in  dilute  alkaline  solution,  when  acted 
on  by  sodium-amalgam,  yields  Maly's  Hydro-biliridin,  a  red  body  insoluble  in 
water,  of  which  the  solution  in  absolute  alcohol  shows  before  the  spectroscope  a 
broad  absorption  band,  between  E  and  F.  It  is  supposed  by  its  discoverer  to 
be  identical  with  the  colouring  matter  of  fasces  {stcrcobhjin)  and  with  the 
jtrobilin  of  Jaffe,  from  both  of  which,  however,  it  differs  in  some  particulars. 
The  physiological  origin  and  destiny  of  the  colouring  matter  in  the  bile  is 
known.  It  has  been  observed  that  when  crystalline  ha;moglobin  in  solution 
is  injected  into  the  circulation,  the  rate  at  which  colouring  matter  is  secreted 
by  the  liver  increases  enormously,  and  that  bile  pigment  appears  in  the  urine. 
In  the  intestines  most  of  the  bilirubin  secreted  is  converted  into  stercobilin 
and  discharged,  but  the  chemical  relations  between  it  and  the  excreted  colour- 
ing matters  are  as  yet  uncertain.  Liquids  which  contain  bilirubin  change 
colour  on  the  addition  of  nitric  acid  containing  a  trace  of  nitrous  acid  :  at  first 
green,  the  colour   passes  through   blue,  violet  and  red,    finally   fading   into 


INTESTINAL    DICESTION.  13 

yellow  (j.v  riiiclical  Part,  Section  VI.).  During  the  change  the  liquid 
shows,  when  examineil  spcctroscopicaliy,  first  two  absorption  bands  near  the 
line  D,  which  are  due  to  the  blue  colour  (choUryaiiiii),  and  subsequently  a 
single  band  betwten  b  and  F,  referable  to  the  yellowish  red  colour  (Jalfe's 
chohtdin).  Bilirubin,  or  a  body  undistinguishable  from  it,  occurs  in  tissues  in 
which  blood  has  been  extra vasated  in  rhombohedral  crystals  (called  Ilcema- 
toidin). 

Biliverdin  (C^j  \\^  N,  OJ  occurs  along  with  bilirubin  in  the  bile  of  man 
and  many  animals,  especially  in  those  of  which  the  bile  is  green.  Its  relative 
quantity  increases  in  inanition.  Both  colouring  matters  are  met  with  in  the 
placenta  of  the  bitch. 

Intestinal  Digestion, 

Pancreatic  juice  is  an  alkaline  liquid  resembling  saliva. 
It  is,  however,  of  greater  density,  and  probably  contains  no 
globulin.  It  owes  its  activity  to  two  ferments — a  diastatic 
and  a  peptic — both  of  which  are  contained  in  the  precipi- 
tate which  is  thrown  down  when  pancreatic  juice  is  treated 
with  alcohol.  They  can  be  extracted  either  from  the 
gland  itself  (Hiifner)  or  from  the  precipitate  (v.  Wittich) 
by  glycerine.  From  either  extract  a  substance  is  precipi- 
tated by  alcohol,  which,  at  the  temperature  of  the  body, 
digests  fibrin  and  other  albuminous  bodies  in  alkaline 
liquids,  and  acts  diastatically  on  starch.  This  substance  is 
called  Pancreatin.  It  contains  a  proteid  body,  to  which 
the  name  Trypsin  has  been  given  by  Kuhne,  and  to  which 
its  peptic  property  appears  to  attach  itself.  P^rom  the 
glycerine  extract  a  substance  containing  the  ferments  is 
precipitated  by  alcohol.  Pancreatic  juice  emulsionizes  and 
decomposes  neutral  fats. 

It  has  lately  been  proved  (Heidenhain)  that  the  cell- 
substance  of  the  living  pancreas  is  inert,  but  acquires 
peptic  activity  by  keeping,  and  more  rapidly  when  acted 
on  by  dilute  acids. 

Proteids,  subjected  to  pancreatic  digestion,  split  into 
two  products,  viz.,  a  body  having  globulin  properties, 
and  a  peptone.  The  former  passes  into  a  peptone  (called 
by  Kiihne  antipeptone),  which  undergoes  no  further  change 


14  INTESTINAL   DIGESTION. 

in  the  intestine ;  the  latter  is  decomposed,  yielding  leucin 
and  tyrosin  and  other  products. 

Simultaneously  with  the  changes  which  are  due  to  the 
action  of  the  pancreatic  ferments,  others  go  on  which  are 
associated  with  the  development  in  the  liquid  of  septic 
organisms  (bacteria),  and  with  the  disengagement  of  offen- 
sive odours.  These  are  the  production  of  volatile  bodies, 
Indol  and  Skatol,  the  disengagement  of  CO^  and  CH^ 
from  the  decomposition  of  certain  carbohydrates,  of  H 
from  butyric  acid  fermentation,  &c.  The  products  of 
pancreatic  digestion  of  proteids  are  also  incidents  of  the 
septic  decomposition  of  the  same  bodies,  but  the  former 
process  is  distinguished  from  the  latter  by  its  great 
rapidity. 

The  liquid  which  is  obtained  when  raw  fibrin  is  digested  for  a  few  hours, 
or  at  the  proper  temperature  with  pancreatic  juice  or  sohition  of  pancreatin, 
contains,  after  it  has  been  freed  from  undissolved  residue,  besides  common 
albumin,  alkali-albuminate  and  peptones,  crystalline  organic  bodies,  of  which 
the  most  important  are  Leucin  and  Tyrosin.  To  obtain  them,  the  albumin  is 
first  got  rid  of  by  slightly  acidulating  the  liquid,  boiling  and  filtering.  The 
filtrate  is  then  reduced  to  a  small  bulk  by  evaporation,  and  heated  with  strong 
alcohol  to  precipitate  the  peptone.  On  again  filtering,  an  extract  is  obtained 
in  which,  if  left  to  itself,   Leucin  and  Tyrosin  crystallize. 

Leucin  (Cg  H,3  NOo),  when  pure,  ciystallizes  in  colourless  pearly  scales, 
which  sublime  in  flocks  at  170°  C.  like  oxide  of  zinc.  In  impure  solution  it 
forms  spheroidal  clumps,  which,  under  the  microscope,  are  seen  to  be  made 
up  of  round  grains,  each  of  which  consists  of  fine  needles  radiating  from  a 
centre.  Tyrosin  crystallizes,  on  cooling  from  its  solution  in  boiling  v.ater,  in 
bunches  or  stellate  groups  of  long  slender  needles  ;  it  does  not  sublime  when 
heated. 

Leucin  is  soluble  in  27  parts  of  cold  M'ater  and  in  hot  alcohol.  Tyrosin 
requires  150  parts  of  hot  water  to  dissolve  it.  In  boiling  alcohol  Leucin 
dissolves,  Tyrosin  remains,  so  that  by  means  of  it  the  two  bodies  can  be  sepa- 
rated from  each  other.  Leucin,  when  heated  in  a  sealed  tube  with  fuming 
hydriodic  acid,  yields  ammonic  iodide  and  caproic  acid,  and  is  therefore 
regarded  as  amido-caproic  acid  (Cg  H,3  NOj  +  3HI  =  Cg  H,2  O2  +  NH4 
I  +  2I).  Tyrosin  (Cg  H,,  NO3),  when  acted  on  in  the  same  way,  yields  a  body 
(C9  Hjo  O3)  which  may  be  regarded  as  oxyphenyljDropionic  acid,  having 
ammonic  iodide  and  iodine.  The  physiological  destiny  of  Leucin  is  unknown. 
As  regards  Tyrosin,  the  recent  researches  of  Kiissner  have  shown  that  when 
it  is  introduced  into  the  circulation  it  reappears  in  the  urine  as  such  :  it  cannot 
therefore  be  regarded  as  a  step  in  the  production  of  urea. 


> 


GI.VCOGKN.  15 

/inM  (C-^ll-,  N)  is  (j!)tained  by  ilij^csting  large  quantities  of  allnimin  with 
ox-pancreas  ami  distilling  the  product.  The  distillate  contains  Indol,  which 
may  be  separated  from  it  by  agitating  it  with  its  bulk  of  ether.  Indol  fuses  at 
52°  C.  and  boils  tit  245'  C.  It  is  soluble  in  water,  and  cr}stallizes  from  its 
solution  in  shining  plates.  When  introduced  into  the  circulating  blood  or 
alimentar)- canal,  an  "  indigo-producing  substance  "  appears  in  the  urine.  It 
exists,  under  normal  circumstances,  in  extremely  small  quantity  in  the  in- 
testinal contents. 

S/ca!ol,  a  crystallizable  body  of  offensive  odour,  resembling  Indol,  has  been 
lately  discovered  by  Brieger  as  a  constituent  of  human  faces.     It  has  also      ^ 
been  shown  that  Phenol  (Carbolic  Acid,  Cg  H-»  OH)  is  constantly  present  in      j"" 
fa:ces.  ' 

An  alkaline  liquid,  called  Snccits  cntcriciis,  of  low  specific 
gravity,  is  secreted  by  the  mucous  membrane  of  the  small 
intestine.     Its  dip;estive  properties  are  as  yet  uncertain. 


Glycogen. 

Glycogen,  or  animal  starch,  is  under  normal  conditions 
always  present  in  the  living  cell-substance  of  the  liver  ;  in 
inanition  it  gradually  disappears  ;  it  is  present  in  the  livers 
of  animals  fed  exclusively  on  flesh.  The  glycogen  of  the 
liver  increases  after  each  period  of  digestion.  Its  quantity 
is  in  general  determined  by  the  quantity  of  dextrose-pro- 
ducing material  or  of  lactose  in  the  food,  so  that  these 
sugars  are  the  normal  but  not  the  only  source  of  glycogen. 
The  processes  by  which  glycogen  disappears  from  the  liver 
in  inanition,  and  by  which  it  is  normally  disintegrated  in 
the  animal  organism,  are  not  known.  After  death,  the 
glycogen  of  the  liver  is  converted  into  dextrose  under  the 
influence  of  a  diastatic  ferment. 

Glycogen  or  anivial  s/anh  is  soluble  in  water,  yielding  r.n  opalescent  solu- 
tion. It  is  coloured  brown  or  reddish-brown  by  iodine.  Glycogen  is  ob- 
tained in  quantity,  by  throwing  the  rapidly  comminuted  liver  of  an  animal 
just  killed,  during  the  period  of  gi-eatest  digestive  activity  of  the  organ,  into 
boiling  water  slightly  acidulated  with  acetic  acid.  From  the  pale  yellow 
fdtered  and  concentrated  extract,  glycogen  is  precipitated  by  the  addition  of 
alcohol. 


1 6  INTESTINAL   ABSORPTION. 

Intestinal  Absorption. 

In  intestinal  absorption  the  dissolved  constituents  are 
absorbed  by  the  blood  stream,  the  particulate  by  the 
lacteals.  The  proteids  of  chyle  are  absorbed  partly  as 
peptone,  partly  as  alkali-albuminate.  They  enter  the 
circulation  both  by  the  veins  and  lacteals,  but  it  cannot  be 
stated  in  what  proportion.  It  is  not  known  whether 
coagulable  albumin  is  absorbed  or  not. 

There  is  reason  to  believe  that  most  of  the  dextrose  into 
which  all  carbohydrates  are  converted  in  digestion  is 
absorbed  by  the  veins,  but  direct  evidence  is  wanting  :  the 
remainder  undergoes  the  lactic  acid  fermentation  in  the 
intestine. 

The  fats  are  absorbed  both  as  glycerides  in  the  state  of 
emulsion,  and  as  alkaline  soaps  and  glycerine.  The  absorp- 
tion of  water,  in  consequence  of  which  the  intestinal  content 
becomes  more  and  more  concentrated  as  it  advances, 
takes  place  by  the  capillaries,  and  is  mainly  due  to  "  diffu- 
sion." Consequently  it  may  be  diminished  or  reversed  by 
the  presence  in  the  intestinal  liquid  of  salts  of  high  "  osmo- 
tic equivalent." 

Faeces  consist  of  insoluble  residues  of  food  and  bile,  and 
of  insoluble  salts  ;  particularly  calcic,  magnesic,  and  am- 
monio-magnesic  phosphates.  They  yield  certain  gases, 
viz.,  COo,  marsh  gas  and  a  trace  of  sulphuretted  hydrogen. 
In  human  excrement  a  crystalline  body  called  excretin 
occurs. 

Diffusion  of  liquids. — When  two  liquids  (of  which  one  A  is  water,  the  other 
B  a  solution)  are  separated  by  a  membrane,  an  exchange  takes  place  between 
them  through  the  membrane.  So  long  as  the  two  liquids  remain  unaltered 
(as  would  be  the  case  if  the  liquid  on  either  side  of  the  membrane  were  con. 
tinually  replaced  by  fresh  of  the  same  quality)  the  relation  between  the  weight 
of  water  which  passes  from  A  to  B,  and  of  the  body  in  solution  which  passes 
from  B  to  A,  is  constant.  This  relation  is  called  the  osmotic  equivalent.  If 
B  holds  NaCl  in  solution,  the  former  is  greater  than  the  latter,  and  the 
equivalent  is  said  to  be  positive  ;  if  IICl,  it  is  less,  and  the  equivalent  is 
said  to  be  negative. 


BLOOD. 


17 


Blood. 

Blood  is  an  opaque  fluid  mass,  each  cubic  millimeter  of 
which  contains  some  five  millions  of  corpuscles  floating  in 
an  alkaline  liquid.  Of  these  about  one  in  400  are  colour- 
less. In  circulating  blood  the  corpuscles  are  equally- 
distributed.  Out  of  the  living  body,  blood  coagulates,  that 
is,  separates  into  clot  and  serum  ;  or,  if  coagulation  is 
prevented  by  a  freezing  temperature,  into  corpuscles  and 
plasma.  If  blood  is  agitated  before  coagulation,  the  fibrin 
is  collected  on  the  agitating  surfaces,  and  thus  separated 
from  the  cruor.  The  coagulum  varies  in  character  accord- 
ing to  the  number  of  corpuscles,  the  time  occupied,  and 
the  form  of  the  recipient.  It  consists  essentially  in  the 
concretion  of  the  plasma  into  a  felt-work  of  transparent 
fibres,  each  of  which  is  scarcely  a  micromillimeter  in  width, 
and  shortens  immediately  after  it  is  formed.  In  the  circu- 
lating blood  coagulation  is  prevented  by  the  influence 
upon  it  of  the  living  tissues,  with  which  it  is  in  relation. 
If  blood  is  received  into  non-contaminated  vessels,  coagu- 
lation is  delayed  or  prevented.  It  is  not  dependent  on  the 
access  or  escape  of  any  gas  or  vapour.  It  is  indefinitely 
deferred  at  0°  C,  most  accelerated  at  40°  C.  By  subsidence 
at  about  6'  C.  blood  separates  into  plasma  and  corpuscles, 
of  which  the  weights  in  normal  human  blood  are  nearly 
equal.  It  contains  three  albuminous  substances,  viz. :  (i) 
common  albumin  ;  (2)  a  little  alkali-albumin  ;  and  (3)  the 
substance  which  becomes  fibrin.  Plasma  coagulates  at 
ordinary  temperatures,  becoming  gelatinous  if  diluted, 
yielding  a  fim  clot  of  fibrin  if  concentrated.  The  substance 
which  thus  assumes  the  solid  form  is  called,  in  its  dissolved 
state,  plasmin,  or  the  substratum  of  coagulation.  It  has 
the  properties  of  a  globulin.  Two  kinds  of  globulin  exist  in 
the  plasma,  one,  named  fibrinogen,  in  very  small  quantity 
(o"3  per  cent.),  which  disappears  in  the  act  of  coagulation  ; 
the  other,  which  is  much  more  abundant,  and  may  consti- 

C 


1 8  COAGULATION. 

tute,  according  to  recent  researches,  more  than  a  third  of 
the  total  weight  of  proteid. 

Serum  albumin  is  soluble  in  water,  and  is  not  precipitated  either  by  dilute 
acids,  by  alkaline  carbonates,  or  by  NaCl.  As  it  exists  in  the  blood,  it  is  pre- 
cipitated by  boiling  or  by  addition  of  alcohol.  It  is  Itevorotatoiy,  and  differs 
from  albumin  of  egg,  in  not  being  coagulated  by  ether,  and  in  being  more 
soluble  in  HCl.  Serum  albumin  can  be  separated  from  the  soluble  salts, 
which  are  present  in  the  serum,  by  prolonged  diffusion  with  water.  In  this 
state,  however,  its  properties  are  altered  ;  it  is  neither  coagulated  by  heat,  nor 
precipitated  by  alcohol. 

Globulins. — The  globulins  are  distinguished  from  common  serum  albumin 
by  the  fact  that  while  insoluble  in  concentrated  solutions  of  neutral  salts, 
particularly  NaCl  and  MgS04  and  in  distilled  water,  they  are  soluble  in 
weak  solutions  :  they  are  also  soluble  in  dilute  alkalies.  They  are  all 
coagulable  by  heat,  but  at  different  temperatures. 

Paraglobidin  is  the  precipitate  pi-oduced  in  serum  by  saturating  it  with 
NaCl  or  MgS04,  or  by  diluting  it  and  then  neutralizing  with  acetic  acid,  or 
by  passing  through  it  a  current  of  COj.  This  precipitate  is  soluble  in  one 
per  cent,  solution  of  NaCl  and  coagulates  at  73°  C.  It  is  contained,  along 
with  serum  albumin,  in  all  the  tissues  and  liquids  of  the  body. 

Fibrinogen  is  distinguished  from  paraglobulin  by  the  greater  difficulty  with 
which  it  is  precipitated  by  dilution  in  neutral  solution.  It  is  contained  in  all 
the  coagulable  liquids.  Its  solution  in  NaCl  is  coagulated  by  heat  at  55°  C. 
(Hammarsten). 

Fibrin  differs  from  fibrinogen  in  its  filamentous  stracture,  and  its  solubility 
in  dilute  NaCl  solution.  Like  myosin,  it  is  soluble  in  strong  solutions  of 
NaCl,  but  with  great  difficulty  :  the  solution  coagulates  at  about  60°  C. 
It  is  convertible  with  difficulty  by  acids  or  by  alkalies  into  albuminate. 
Crude  fibrin  decomposes  solution  of  H2O2 :  it  is  converted  by  boiling  into  a 
body  resembling  coagulated  albumin. 

The  liquids  contained  in  uninflamed  serous  cavities, 
which  coagulate  imperfectly  (pericardial  fluid)  or  not  at 
all  (hydrocele  fluid),  also  contain  both  forms  of  globulin. 
These  liquids  for  the  most  part  coagulate  on  the  addition 
of  serum.  Their  percentage  of  fibrin-yielding  material  is, 
however,  small. 

From  blood  which  has  been  a  short  time  withdrawn 
from  the  circulation  a  ferment-like  substance  can  be 
prepared,  the  solution  of  which,  although  it  contains  no 
globulin,  promotes  the  coagulation  of  coagulable  fluids. 

In  coagulation  many  of  the  colourless  corpuscles  of  the 


BLOOD-DISKS.  I9 

blood  undergo  disintegration  :  it  is  believed  that  they 
take  an  important  part  in  the  process,  and  even  contribute 
the  materiaLout  of  which  fibrin  is  formed.  They  appear 
also  to  be  the  source  of  the  ferment  above  mentioned,  for 
plasma  filtered  at  a  few  degrees  above  o''  C.  loses  its  power 
of  coagulating  at  ordinary  temperatures :  this  power  is 
restored  to  it  by  the  addition  of  a  ferment,  but  the  quan- 
tity of  fibrin  obtained  is  less  than  that  yielded  by  unfil- 
tered  plasma. 

The  Plasma  of  blood  contains  about  0*5  per  cent,  of  the 
total  blood-weight  of  soluble  salts,  of  which  between  0*3 
and  04  is  sodic  chloride,  and  about  0"i  sodic  phosphate, 
the  remainder  consisting  chiefly  of  sodic  carbonates.  The 
insoluble  calcic  and  magnesic  phosphates,  of  which  plasma 
contains  about  0*04  per  cent,  of  the  blood-weight,  are  held 
in  solution  by  combination  with  albumin.  Serum  also 
contains  a  trace  of  sulphates. 

Serum,  i.e.,  plasma  which  has  been  deprived  of  its 
plasmin  by  coagulation,  differs  from  plasma  in  the  absence 
of  fibrinogen.  It  contains  serum-albumin,  paraglobulin, 
and  probably  alkali-albuminate,  besides  salts  and  extrac- 
tive. The  whole  of  the  proteid  of  serum  (albumin  and 
globulin),  with  the  exception  of  a  trace  of  albuminate,  is 
separated  by  heat  at  about  73°  C.  It  is  also  precipitated 
by  alcohol  and  by  strong  mineral  acids. 

Plasma  contains  oxygen  and  nitrogen  in  about  the  pro- 
portion in  which  these  gases  are  severally  found  in  water. 
It  contains  somewhat  more  free  CO^than  the  serum  would 
absorb  if  it  were  so  much  water. 

Blood-disks. — The  coloured  blood-corpuscles  consist  of 
stroma  and  haemoglobin.  They  constitute  about  a  third 
of  the  weight  of  the  blood,  and  contain  about  43  per 
cent,  of  solids,  and  39  per  cent,  of  hc-emoglobin.  The 
stroma  is  made  up  for  the  most  part  of  substances  soluble 
in  ether,  viz.,  lecithin  and  cholesterin,  and  of  globulins 
resembling   those  of  plasma.     The  blood-corpuscles  also 

C  2 


20  HEMOGLOBIN. 

contain  inorganic  salts,    which  differ   from   those    of  the 
plasma,  in  the  replacement  of  sodium  by  potassium. 

The  body  of  the  corpuscles  consists  chiefly  of  globulins 
associated  with  lecithin  and  cholesterin.  The  globulin  is  of 
two  kinds,  the  greater  part  resembling  paraglobulin,  the 
remainder  having  the  characters  of  myosin.  The  colour- 
less corpuscles  also  contain  glycogen,  and  are,  like  the 
coloured  corpuscles,  relatively  rich  in  potassic  salts.  The 
nuclei  contain  a  non-crystallizable  nitrogenous  body 
(nuclein — not  a  proteid)  which  is  insoluble  in  weak  acids, 
and  hence  in  gastric  juice,  but  dissolves  very  readily  in 
weak  alkalies.  The  chemical  relations  of  this  substance 
are  as  yet  unknown.  It  is  found  in  all  nuclear  structures, 
e.g.,  in  spermatozoids.  The  "  protoplasm  "  of  the  colour- 
less corpuscles  consists  chiefly  of  globulin  associated  with 
lecithin  and  cholesterin.     It  contains  glycogen. 

In  normal  blood,  haemoglobin  exists  only  in  the  cor- 
puscles, but  in  certain  diseased  states  it  is  dissolved  in  the 
plasma  and  is  then  crystallizable :  the  nature  of  the 
change  it  undergoes  is  not  known.  A  similar  change  is 
produced  artificially  by  repeated  freezing  and  thawing,  by 
subjecting  blood  to  a  temperature  of  60°  C,  or  by  the 
action  of  ether  or  chloroform.  The  property  which  the 
blood  possesses  of  absorbing  oxygen  from  the  inspired  air, 
and  of  giving  it  up  to  the  living  tissues  with  which  it  is 
brought  into  contact  in  the  circulation,  is  due  to  its 
haemoglobin. 


TTczmoglobm  crystallizes  from  its  solution,  in  forms  which  vary  according  to 
the  animal  from  which  it  is  derived.  The  crystals  are  of  the  colour  of 
arterial  blood,  but  become  dark,  without  changing  their  form,  when  placed 
in  vacuo  at  a  low  temperature.  They  then  exhibit  two  colours,  looking  green 
along  the  edges,  purplish-red  elsewhere  :  on  the  admission  of  air  or  oxygen, 
the  colour  is  restored. 

Haemoglobin  is  very  soluble  in  warm  water,  much  less  so  in  cold,  but,  in 
this  respect,  crystals  oljtained  from  different  animals  differ :  thus,  the  hcemo- 
globin  of  the  rat  or  guinea-pig  is  less  soluble  than  that  of  man,  and  is  much 
more  prone  to  crystallize. 


BLOOD  GASES.  21 

Hsemoglobin  contains  -g-j-g-  of  its  weight  of  iron.  Solution  of  hcuinoglobin 
exhibits  before  the  spectroscope  characteristic  absorption  bands.  Very  dilute 
solution  shows  ope  band  to  the  blue  side  of  the  D  line  ;  if  the  solution  is 
stronger,  a  second  band  appears  to  the  red  side  of  the  E  line  ;  by  still  more 
concentrated  liquids,  the  blue  and  violet  rays  are  entirely  absorbed,  while 
the  two  bands  become  confluent. 

When  blood  is  allowed  to  stand  at  ordinary  temperatures,  its  hemoglobin 
is  soon  decomposed,  yielding  hrematin,  a  proteid  body,  and  other  products. 
The  same  thing  happens  much  more  rapidly  when  solution  of  hamioglobiu  is 
acted  on  by  alkalies,  in  which  case  hacmatin  and  alkali-albuminates  are 
formed.  In  presence  of  weak  acids,  haemoglobin  yields  hxmatoin  (so-called 
"acid  hcematin  ")  and  acid  albuminate. 

Hamatin  (C3,  H34  N4  Fe  O^)  is  obtained  when  weak  potash  solution  acts 
on  blood  or  solution  of  hemogloljin  7inth  access  of  air.  On  neutralizing,  solid 
hsematin  is  precipitated.  It  is  insoluble  in  water,  alcohol,  and  ether,  and 
uncrj'stallizable. 

The  absorption  spectrum  of  hcematin  presents  a  broad  band  to  the  red  side 
of  the  U  line.  After  reduction  by  alkaline  sulphides  it  shows  two  charac- 
teristic bands,  one  in  the  yellow,  the  other  in  the  green  part  of  the  spectrum. 
When  dried  blood  is  warmed  with  glacial  acetic  acid,  it  yields  crj'stals  of 
ha:viin  (hrematin  +  HCl). 

Solution  of  hremoglsbin  associates  nitric  oxide  and  carbonic  oxide  in  the 
same  volume  as  oxygen.  When  oxygenated  solution  of  htemoglobin  or  of 
blood  is  acted  on  by  carbonic  oxide,  its  associated  oxygen  is  replaced  by  that 
gas.  The  solution  acquires  a  colour  which  closely  resembles  that  of  arterial 
blood,  but  is  not  affected  by  reducing  agents. 


The  quantity  of  oxygen  yielded  to  the  barometer  vacuum 
by  any  quantity  of  aerated  defibrinated  blood  is  equal  to 
the  quantity  associated  by  the  haemoglobin  contained  in 
the  blood, ////J  the  quantity  absorbed  by  the  plasma;  (hence 
for  every  5  centigrammes  of  iron  187  cubic  centimeters 
of  oxygen  at  0°  and  760  m.m.)  In  ordinary  arterial  blood 
the  yield  of  oxygen  is  a  little  less.  Arterial  blood  at 
40°  yields  about  40  per  cent,  of  its  volume  of  COg,  as 
measured  at  0°  and  760  m.m.  The  alkaline  carbonates  are 
decomposed  in  the  vacuum  without  the  addition  of  an  acid. 

The  human  body  contains  about  -^  of  its  weight  of 
blood. 

In  the  examination  of  blood  for  clinical  purposes,  it  is 
chiefly  important  to  determine  the  percentage  of  haemo- 
globin and  the  alkaline  reaction. 


22  THE   SPLEEN. 

Arterial  blood  becomes  venous  by  contact  with  living 
protoplasm.  Venous  blood  is  distinguished  from  arterial 
by  its  crimson  colour,  its  slight  dichroism,  the  less  propor- 
tion of  oxygen  which  is  associated  with  its  haemoglobin,  its 
large  proportion  of  combined  CO2,  its  less  proneness  to 
coagulation,  and  by  containing  fewer  blood-corpuscles. 
Venous  blood  differs  somewhat  in  composition  according  to 
its  source.  As  compared  with  ordinary  venous  blood,  that 
of  the  hepatic  vein  contains  less  albumin  and  more  ex- 
tractives {e.g.,  urea  and  grape-sugar).  In  that  of  the  splenic 
vein,  also,  differences  exist,  which  indicate  that  in  this 
organ  the  coloured  blood-corpuscles  are  disintegrated,  and 
colourless  corpuscles  formed. 


The  Spleen. 

The  following  are  the  facts  best  ascertained  as  to  the 
spleen-pulp,  and  the  blood  which  flows  from  it : — 

The  spleen-pulp  contains  much  haemoglobin,  to  which 
the  richness  of  its  ash  in  iron  is  due  (Malassez),  The 
aqueous  extract  of  spleen-pulp  contains  uric  acid,  and  the 
allied  body  hypoxanthin,  in  quantities  which,  although 
very  small,  are  larger  than  those  met  with  in  any  other 
tissue  (Strecker).  The  splenic  blood  contains  fewer  blood- 
disks  and  more  colourless  corpuscles  than  the  blood  of  any 
other  organ.  There  exist  in  the  spleen  structures  which 
are  destined  to  become  colourless  corpuscles.  It  also  con- 
tains structures  which  are  concerned  in  the  breaking  up  of 
blood-disks,  and  are  the  sources  of  the  pigment  with  which 
the  pulp  is  provided.  The  enlargement  of  the  spleen 
which  takes  place  a  few  hours  after  every  considerable 
meal,  is  chiefly  if  not  entirely  due  to  vascular  dilatation 
(Mosler). 


chemical  process  of  respiration.  23 

Lymph. 

Lymph  or-tissLic  juice  resembles  blood  in  being  coagu- 
lablc  and  in  containing  colourless  corpuscles.  It  differs 
from  it  in  being  of  lower  specific  gravity,  in  the  tardiness 
with  which  it  coagulates,  in  the  absence  of  blood-disks,  and 
consequently  of  haemoglobin,  and  in  its  containing  rela- 
tively to  its  weight  less  proteid,  more  urea  and  other 
extractives,  more  sodic  carbonates,  and  in  yielding  to  the 
mercurial  vacuum  more  CO^.  Its  corpuscles  arc  derived 
partly  from  the  tissues,  but  chiefly  from  the  lymphatic 
glands. 

Chyle  differs  from  lymph  chiefly  in  respect  of  the  larger 
proportion  of  fat  (about  i  per  cent.)  which  is  present  in  it. 
Each  of  the  minute  granules  to  which  chyle  owes  its 
opacity  consists  of  a  fat  particle  enclosed  in  an  envelope 
of  proteid. 


Chemical  Process  of  Respiration. 

In  respiration  each  quantity  of  air  respired  undergoes 
the  following  changes  : — Its  oxygen  is  diminished  by  about 
a  quarter,  viz.,  from  21  per  cent,  to  16  per  cent.  Its  CO2 
is  increased  a  hundred-fold,  viz.,  from  about  004  per  cent, 
to  over  4  per  cent  It  becomes  nearly  saturated  with 
moisture.  It  acquires  nearly  the  temperature  of  the  body. 
It  becomes  more  or  less  charged  with  organic  impurity, 
acquiring  thereby  a  peculiar  smell.  Its  volume  is  dimin- 
ished by  -oio  or  thereabouts.  Its  weight  is  increased  in 
proportion  to  the  weight  of  CO^  discharged. 

The  percentage  of  COo  is  dependent  on  the  length  of 
time  that  the  expired  air  has  remained  in  the  respiratory 
cavity.  (It  can  be  increased  by  voluntary  retention  to  7*5 
per  cent.)  Consequently,  as  the  frequency  of  respiration 
increases  the  percentage  diminishes,  though  the  total  dis- 
char^ie  increases. 


24  CHEMICAL  PROCESS 

Example  : — 

Frequency 6  24  48 

Cubic  centims  of  COj  per  minute 171         396  696 

,,  ,,         ,,         per  respiration      28"S         i6"5  I4'5 

(Vierordt). 

The  frequency  remaining  the  same,  the  CO^  increases 
with  the  amphtude  of  the  respirations. 
Example  : — 
Frequency — 12  respirations  per  minute. 

Amplitude.  COj  per  min.  (c.c.)  Percentage. 

3  Litres  162  5*4 

6      „  240  4-5 

12      ,,  480  4'0 

24      ,,  816  3 '4  (Vierordt). 

In  the  compressed  air  chamber  the  respirations  become 
more  ample  and  the  CO2  discharge  increases. 

Respiratory  exchange  of  gases. — If  a  liquid  is  exposed  to 
a  gas,  the  former  absorbs  the  latter  until  equilibrium  is 
established.  As  soon  as  this  is  the  case  the  tension  of  the 
gas  in  the  liquid  is  said  to  be  equal  to  its  tension  outside  of 
it.  If  a  liquid  is  exposed  to  a  gaseous  mixture,  the  ab- 
sorption of  each  gas  takes  place  as  if  there  were  no  other. 
If  a  very  small  volume  of  a  gaseous  mixture  is  exposed  to 
an  indefinitely  large  volume  of  a  liquid  containing  gases, 
the  latter  will  be  absorbed  from,  or  given  off  into  the 
former  until  the  tension  of  each  gas  in  the  mixture  is  equal 
to  its  tension  in  the  liquid.  When  in  this  experiment  the 
liquid  is  the  circulating  blood,  and  the  mixture  atmospheric 
air,  the  oxygen  of  the  latter  diminishes,  for  the  tension  of 
oxygen  in  such  blood  scarcely  amounts  to  30  millimeters 
(=i2V  atmosphere),  while  the  CO^  increases  until  its  tension 
amounts  to  about  40  millimeters. 

The  tension  of  carbonic  acid  in  the  air  contained  in  the 
air  cells  is  so  little  inferior  to  that  of  ordinary  venous 
blood,  that  the  discharge  of  CO^  would  probably  be  in 


OF    RESPIRATION.  2$ 

sufficient,  unless  the  COo  tension  were  greater  in  the 
pulmonary  capillaries  than  anywhere  else  in  the  circulation. 
The  nature  of  the  agency  by  which  this  is  brought  about 
is  indicated  by  the  fact  that  the  addition  of  oxygenated 
hcTemoglobin  to  serum  in  v^acuo  decomposes  its  carbonates, 
setting  free  CO.,,  so  that  venous  blood  yields  more  CO^  to 
oxygen  than  to  the  barometer  vacuum.  Consequently  the 
discharge  of  CO.,  in  pulmonary  respiration  is  directly  pro- 
moted by  the  absorption  of  oxygen. 

Respiration  can  be  maintained  without  difficulty  in  an 
atmosphere  which  contains  much  less  than  the  normal  pro- 
portion of  oxygen,  so  that  an  animal  supplied  with  a  limited 
quantity  of  air  continues  to  breathe  in  it  until  it  has  used 
all  but  a  fraction  of  the  oxygen  it  contains. 

The  process  by  which  the  circulating  blood  gives  oxygen 
to  the  living  protoplasm  with  which  it  comes  into  relation 
in  the  capillary  blood-vessels,  and  receives  COg,  is  often 
called  "  internal  respiration."  The  existence  of  such  an 
exchange  of  gases  in  the  tissues  is  proved  by  the  obser- 
vation that  venous  blood  differs,  in  the  proportion  of  oxy- 
gen and  COo  which  it  contains,  according  to  the  tissue 
through  which  it  has  circulated. 

The  separation  of  CO2  by  protoplasm,  and  the  absorption 
of 'Oxygen,  are  distinct  and  independent  processes,  and  do 
not  go  on  pari  passu.  The  former  is  variable  ;  its  variations 
are  dependent  on  the  functional  activity  of  the  tissue  ;  the 
latter  is  constant  and  is  associated  with  restitution.  The 
independence  of  the  two  processes  is  proved  (i)  as  regards 
muscular  tissue,  by  the  observation  that  muscle  which  has 
been  entirely  deprived  of  oxygen  can  be  thrown  into 
functional  activity  {i.e.,  contraction)  without  receiving  any 
supply,  and  that  in  contracting  it  gives  off  COo  (Hermann)  ; 
and  (2)  as  regards  the  entire  organism,  by  the  observation 
that  a  frog,  if  kept  at  a  low  temperature,  continues  to  dis- 
charge CO.^  at  nearly  the  normal  rate,  in  an  atmosphere  of 
pure  nitrogen  (Pfluger). 


26  URINE. 

In  the  investigation  of  the  chemical  process  of  respiration 
in  man  or  the  lower  animals,  three  quantities  are  to  be 
determined,  viz.,  the  discharge  of  COg,  the  absorption  of 
oxygen,  and  the  discharge  of  water.  In  the  most  complete 
methods  {e.g.,  that  of  Regnault  and  Reiset)  all  three  are 
determined.  In  Pettenkofer's  method,  the  CO2  and  HgO 
discharge  only  are  determined  ;  but  the  method  has  the 
advantage  of  being  applicable  to  large  animals  and  to  man. 

Urine. 

The  average  daily  discharge  of  urine  of  an  adult  male  on 
full  diet  is  1500  grammes,  containing  about  36  grammes  of 
urea,  o"j  gramme  of  uric  acid,  16  grammes  of  sodic 
chloride,  and  about  6  grammes  of  other  inorganic  salts, 
besides  colouring  matter  and  other  organic  constituents. 
Hence  urine  contains  about  4*0  percent,  of  solids,  including 
2-4  per  cent,  of  urea.  Its  acidity  is  equal  to  that  of  a  0'2 
per  cent,  solution  of  oxalic  acid. 

The  salts  of  the  urine  are,  common  salt,  potassic  chloride, 
sodic,  calcic,  and  magnesic  phosphates  ;  and  sodic  and 
potassic  sulphates.  The  discharge  of  sodic  chloride  varies 
with  the  store  of  chlorine  in  the  body.  It  is  markedly 
diminished  by  abnormal  transudation  of  blood  plasma. 

The  discharge  of  alkaline  phosphates  also  varies  with  the 
quantity  stored  in  the  blood  plasma  ;  that  of  earthy  phos- 
phates with  the  disintegration  of  proteids  of  food.  Hypo- 
sulphites and  sulphates  occur  in  the  urine  as  results  of  a 
process  of  oxidation  which  has  its  seat  in  the  kidneys,  for 
sulphates  are  met  with  only  in  traces  in  the  blood  or  tissues. 
Of  the  two  alkaline  bases  about  8  grammes  (reckoned  as 
potash  and  soda)  are  discharged  daily,  the  soda  constituting 
a  little  more  than  half  In  fever  and  all  conditions  attended 
with  increased  disintegration  of  tissue  or  blood-corpuscles, 
the  proportion  of  potash  is  larger.  If  carbonates  exist  in 
the  urine  they  are  derived  from  the  oxidation  of  vegetable 
acids  used  as  food. 


UREA.  27 

Urine,  if  uncontaminatcd,  may  be  kept  for  an  indefinite 
period  withoiU:  any  change,  excepting  that  its  acidity  and 
colour  increase  shghtly  soon  after  it  is  passed  (acid  fermen- 
tation). Under  ordinary  circumstances  urine  becomes 
eventually  alkaline  when  kept,  in  consequence  of  the  pro- 
duction of  ammonic  carbonate.  This  change  takes  place 
rapidly  in  presence  of  a  ferment  which  exists  in  the  urine 
in  certain  pathological  conditions.  The  alkaline  fermen- 
tation is  attended  by  the  formation  of  triple  phosphate. 

It  is  by  the  discharge  of  urea  that  the  rate  at  which 
nitrogen  is  discharged  from  the  organism  is  estimated. 
Thus  we  learn  that  the  discharge  of  nitrogen  is  subject  to 
regular  diurnal  variations  ;  that  it  is  largest  when  food  is 
albuminous  and  abundant  ;  that  it  is  diminished  rapidly 
by  inanition,  gradually  by  a  diet  containing  a  large 
proportion  of  carbonic  hydrates  ;  that  it  is  increased  by 
ingestion  of  water,  sodic  chloride,  and  ammonium  salts, 
and  that  it  is  very  slightly  augmented  by  muscular  exer- 
cises. 

Urea  exists  in  all  the  animal  liquids,  and  in  most  tissues, 
excepting  the  muscular  and  nervous,  in  a  proportion  not 
exceeding  0*03  per  cent.  This  proportion  is  increased  by 
any  interference  with  the  renal  excretion.  Urea  is  a  direct 
product  of  the  life  of  protoplasm.  It  is  not  as  yet  proved 
that  it  is  more  actively  produced  in  the  liver  than  else- 
where. 

Crystalline  Organic  Bodies  ov  the  Urine. 

[^ua  or  Carbamide  (CO  (NHj)^)  exists  as  such  in  urine — so  abundantly  in 
that  of  the  carnivora,  that  it  ciystallizes  therefrom  on  evaporation.  In  human 
urine  it  can  be  crystalUzed  from  the  alcoholic  extract  of  the  dry  residue. 
Urea  (U)  is  excessively  soluble  in  water,  soluble  in  alcohol,  insoluble  in  ether; 
it  is  isomeric  with  ammonic  cyanate  (NHjCNO) ;  takes  up  water  in  contact 
with  certain  ferments,  and  is  transformed  into  normal  ammonic  carbonate 
(CO  (NH2)j+2ll20:=C03  (XH^)^).  A  corresponding  change  occurs  when  U 
is  acted  on  by  alkalies  or  by  strong  sulphuric  acid,  ammonia  being  given  off  in 
the  former  case,  carbonic  anhydride  in  the  latter.  On  the  addition  of  nitric 
acid  to  strong  solution  of  U,  a  snow-white  precipitate  is  formed  of  Urea-nitrate 
(U,  NO3  H),  consisting  of  rhombic  plates  having  a  characteristic  imbricated 


28  URIC   ACID. 

aiTangemcnt  and  mother-of-pearl  lustre.  Oxalic  acid  acts  similarly,  producing 
Urea-oxalate  (U,  Cj  Hj  O4),  but  the  crystals  are  not  so  characteristic.  Both 
bodies  are  quite  insoluble  in  the  acid  liquids.  An  important  compound  (2U-j- 
Hg  (N03)o+3Hg  0)is  obtained  as  a  heavy  amorphous  white  precipitate,  when 
a  dilute  solution  of  U  is  acted  upon  by  dilute  solution  of  mercuric  nitrate  in 
excess.  This  body  is  insoluble  in  neutral  or  slightly  acid  liquids,  but  soluble 
in  nitric  acid.  On  adding  sodic  carbonate  to  the  solution  it  is  precipitated. 
Hence,  if  a  solution  of  mercuric  nitrate  of  known  strength  is  added,  drop  by 
drop,  to  a  solution  of  U  acidulated  with  nitric  acid,  and  the  mixture  tested 
from  time  to  time  by  mixing  a  drop  of  it  with  a  drop  of  sodic  carbonate, 
such  mixture  will  be  attended  with  the  formation  of  an  additional  white 
precipitate,  so  long  as  there  remains  any  uncombined  urea.  The  moment 
that  all  has  been  used  up,  the  test  will  indicate  the  presence  of  excess  of 
mercuric  nitrate  in  the  mixture,  by  the  formation  of  a  precipitate  of  basic 
nitrate. 

Uric  acid  exists  in  urine  chiefly  as  an  acid  sodium  salt 
which  is  deposited  in  the  cold.  When  this  is  decomposed 
by  a  stronger  acid  the  free  acid  crystallizes.  Ammonium 
urate  occurs  only  in  ammoniacal  urine.  Uric  acid  is 
absent  in  the  urine  of  herbivorous  mammalia,  but  in  that 
of  birds  and  reptiles  it  takes  the  place  of  urea  as  the 
channel  for  the  discharge  of  nitrogen.  In  man  it  is  dis- 
charged in  relatively  larger  quantities  in  early  infancy  than 
in  adult  life  ;  its  relative  proportion  to  urea  is  increased  a 
few  hours  after  a  full  meal. 

The  daily  discharge  of  uric  acid  is  increased  by  certain 
kinds  of  dyspepsia,  in  fever,  and  in  certain  chronic  diseases. 
It  undergoes  oxidation  into  urea  and  oxalic  acid  in  the 
body. 

Uric  Acid  (C5  H4  N4  O3,  also  called  lithic  acid)  being  soluble  in  water  only 
in  the  proportion  of  one  part  to  14,000,  exists  as  such  in  extremely  small  quan- 
tities in  urine.  Uric  acid  crystallizes  readily  in  urine  to  which  enough 
hydrochloric  acid  has  been  added  to  decompose  its  urates.  The  most  common 
forms  of  crystals  are  the  so-called  whetstone  crystals  and  the  sheaf-like  bundles 
of  flattened  needles,  which  (as  formed  in  urine)  are  always  of  an  amber  brown 
colour.  Acid  sodic  urate  (Cg  Hj  N4  O3,  HNa)  is  always  present  in  normal 
urine.  In  urine  of  which  the  urea  has  undergone  transformation  into  amnionic 
carbonate,  ammonic  urate  (C;,  H.,  N4  O3,  NH4)  is  deposited  in  needle-shaped 
crystals  which  are  often  in  stellate  groups.  In  ordinary  urine,  when  concen- 
trated by  evaporation  and  then  cooled,  an  amorphous  deposit  falls,  which 
consists  chiefly  of  sodic  urate.  The  same  body  often  occurs  as  a  natural 
subsidence  in  disease   (lateritious  sediment).      Uric  acid  and   urates  reduce 


iiirruRic  ACID.  29 

cupric  oxide  ami  other  metallic  oxides  and  salts.  When  uric  acid  is  moistened 
with  nitric  acid,  the  excess  of  acid  gently  evaporated,  and  the  residue  after 
cooling  breathed  on,  and  then  held  over  strong  ammonia,  a  bright  red  colour 
is  produced,  which  is  due  to  the  formation  of  murexide  ;  if  potash  or  soda  be 
added  instead  of  ammonia,  the  colour  produced  is  violet. 

AllaJitoin  exists,  along  with  uric  acid  and  urea,  in  the 
urine  discharged  during  the  first  few  days  of  life. 

Hippuric  acid,  which  in  the  urine  of  many  herbivorous 
mammalia  replaces  uric  acid,  also  occurs  in  human  urine 
in  very  small  proportion.  It  is  of  importance  as  affording 
a  channel  for  the  discharge  of  glycin  from  the  organism. 
Taurin,  in  like  manner,  appears  in  the  urine  as  Tauro- 
carbamate.  The  body  cystic  oxide  or  cystiti,  which  also 
contains  sulphur,  occurs  occasionally  either  as  a  crystalline 
deposit  or  as  a  concretion.  Its  physiological  relations  are 
unknown. 

Ilippiirk  acid  (C9  lig  NO,)  occurs  in  very  small  proportions  (less  than  0"l 
per  cent. )  in  human  urine  or  in  that  of  the  carnivora,  but  so  abundantly  as 
alkaline  hippurates  in  that  of  herbivora,  that  on  the  addition  of  hydrochloric 
acid  it  crystallizes  out.  It  is  obtained  by  boiling  the  urine  of  the  horse  or  the 
cow  with  milk  of  lime,  filtering,  concentrating  the  filtrate,  and  adding  hydro- 
chloric acid.  It  crystallizes  in  four-sided  prisms,  which  have  their  edges  bevelled 
off  at  the  ends.  Hippuric  acid  is  scarcely  soluble  in  cold  water,  more  readily 
in  hot,  but  its  salts  are  very  soluble.  It  appears  in  the  urine  of  man  and 
other  non-herbivorous  animals,  whenever  benzoic  acid  (C,  Hg  O^)  enters  the 
organism,  glycin  being  taken  up  and  water  given  off.  C7  Hg  Oj-l-Cj  IL,  (NII5) 
Oa=C.j  H9  NOj-f  II5  O.  On  the  other  hand,  it  very  readily  undergoes  decom- 
position, yielding  benzoic  acid  and  glycin  whenever  urine  containing  it  becomes 
putrid.  In  the  formation  of  hippuric  acid  from  benzoic  acid  in  the  living 
organism  the  glycin  produced  in  the  liver  takes  part,  but  it  has  not  yet  been 
proved  that  the  process  by  which  it  is  normally  produced  in  such  large 
quantity  in  herbivora  is  of  the  same  kind  ;  it  has,  however,  been  shown 
that  sufficient  sources  of  benzoyl  exist  in  the  food  of  such  animals.  As 
regards  the  origin  of  hippuric  acid  in  the  carnivora  and  in  man  nothing  is 
known.  In  all  animals  of  which  the  urine  contains  much  hippuric  acid  {i:.g., 
in  the  horse),  "  indigo-producing  substance"  is  also  present  in  relatively  large 
quantities. 

The  urine  also  contains  an  organic  base,  creatinin,  the 
percentage  of  which  depends  upon  the  quantity  of  crcatin 
taken  as  food. 


30  COLOURING   MATTER. 

Creatinin  is  an  alkaline  body  Avhich  exists  in  small  quantity  (abotit  O'l  per 
cent. )  in  urine.  It  is  soluble  in  cold  water,  still  more  so  in  hot.  From  its 
solution  in  boiling  alcohol  it  ciystallizes  on  cooling.  On  the  addition  of 
syrupy  solution  of  zinc  chloride  to  its  aqueous  solution,  characteristic  warty 
clumps  are  formed  of  the  combination  of  zinc-chloride  ((C4  H7  Ng  0)2  Zn  CU) 
and  creatinin,  each  of  which  is  seen  under  the  microscope  to  consist  of 
acicular  ciystals  radiating  from  a  centre  {see  Creatin,  p.  32). 

Human  urine  contains  a  soluble  yellow  colouring  matter 
(urochrome)  which  is  precipitated  from  its  solution  by 
acetate  of  lead  ;  it  also  usually  contains  a  colourless  chro- 
mogenous  substance,  which  when  treated  with  hydro- 
chloric acid  yields  indigo-blue.  Grape-sugar  exists 
normally  in  urine,  but  in  very  small  quantity.  As,  how- 
ever, both  uric  acid  and  creatinin  reduce  cupric  oxide,  the 
presence  of  sugar  cannot  be  proved  by  the  copper  test 
unless  these  bodies  have  been  previously  removed. 

The  yellozv  colouring  matter  of  the  urine  is  obtained  by  treating  the  liquid 
with  milk  of  lime,  and  allowing  it  to  stand.  After  separation  of  the 
deposit,  the  clear  filtrate  is  precipitated  by  solution  of  plumbic  acetate  to 
which  ammonia  has  been  added.  The  lead  precipitate,  having  been  treated 
with  just  sufficient  sulphuric  acid  to  decompose  it,  yields  a  yellow  solution, 
which  owes  its  colour  to  a  body  to  which  the  name  tirochrome  was  given  by 
Thudichum.  This  body  is  soluble  in  water,  insoluble  in  alcohol.  Its  solution 
exhibits  no  absorption  bands  before  the  spectroscope.  On  boiling  it  for  some 
hours  with  sulphuric  acid,  various  brown  or  black  substances  are  formed,  the 
most  characteristic  of  which  (called  iironielanine)  is  soluble  in  ammonia,  and 
is  re-precipitated  on  neutralizing  the  solution  with  sulphuric  acid.  Of  the 
chemical  relations  of  urochrome  little  is  known. 

Indigo-forming  substance. — Urine  (particularly  that  of  the  horse)  when 
mixed  with  half  its  volume  of  strong  hydrochloric  acid,  becomes  dark,  and 
after  some  hours  exhibits  a  scum  or  sediment  which  contains  indigo-blue 
(Cg  ri,  NO).  If  this  scum  is  collected  on  a  filter  and  treated  with  ammonia, 
a  blackish  substance  with  which  it  is  mixed  is  dissolved  and  removed.  If 
after  washing  the  filter  with  cold  alcohol  (which  dissolves  out  a  red  colour) 
the  filter  and  residue  are  boiled  in  the  same  solvent,  a  beautiful  blue  solution 
is  obtained,  which,  on  cooling,  deposits  flocks  of  indigo-blue. 

The  materials  which  constitute  urinary  deposits  and 
concretions  may  be  divided  into  those  of  acid  and  of 
alkaline  urine,  the  former  comprising  uric  acid,  urates,  and 
calcic  oxalate,  the  latter  the  calcic  and  magnesic  phos- 
phates, triple  phosphate,  and  calcic  carbonate. 


muscular  tissue.  31 

Muscular  Tlssue. 

Muscular  substance  consists  chiefly  of  a  globulin  named 
Diyosiii,  which  differs  little  from  fibrinogen.  This  body  is 
fluid  in  living  muscle,  but  coagulates  when  life  ceases. 
Frozen  muscle  carefully  thawed,  yields  a  juice  which 
coagulates  (whether  with  the  aid  of  a  ferment  is  not 
known)  at  ordinary  temperature.  The  coagulum  dissolves 
readily  in  salt  solution. 

Muscle  contains,  in  addition  to  myosin,  serum-albumin 
and  other  proteids  which  coagulate  at  lower  temperatures. 
The  aqueous  extract  of  dead,  i.e.  coagulated,  muscle  con- 
tains a  free  acid  {smrolactic)  which  is  not  present  during 
life.  The  extract  yields  crcatin  by  direct  crystallization  in 
tlie  proportion  of  about  0"2  per  cent,  of  the  weight  of  the 
muscle  employed.  The  glycogen  Avhich  all  muscle  con- 
tains in  the  perfectly  fresh  state  is  replaced  by  dextrose 
in  dead  muscle.  The  extractive  contains  also  Inosite, 
XaiitJiiii,  HypoxantJiiii,  Tanrin^  and  a  trace  of  uric  acid. 

Myosin  is  obtained  in  quantity  by  thoroughly  washing  comminuted  muscle 
with  water  and  then  treating  the  insoluble  residue  with  strong  salt  solution 
(one  part  of  brine  to  two  of  water),  filtering  the  solution  and  then  precipitating 
by  the  addition  of  salt  in  substance.  It  is  readily  soluble  in  dilute  liCl,  or 
alkalies,  which  soon  convert  it  into  acid  or  alkali-albumin.  Its  solution 
coagulates  in  weak  NaCl  at  55°  to  60°  C. 

Sarcclactic  achi. — A  body  resembling  lactic  acid  of  milk,  even  in  chemical 
structure,  but  differing  from  it  in  being  dextrorotatory',  and  in  the  solubility, 
hydration  and  crystalline  form  of  some  of  its  salts.  It  is  contained  in  the 
alcoholic  extract  of  the  concentrated  water  extract  of  flesh  from  which  the 
creatin  has  been  ciystallized  and  separated.  The  syiiipy  mother  liquor,  after 
treatment  with  sulphuric  acid,  is  extracted  with  ether.  The  ether  extract 
leaves  sarcolactic  acid  on  evaporation. 

Inosite  or  Muscle  sugar  exists  sparingly  in  all  muscle,  and  occurs  patho- 
logically in  the  urine  in  urxmia  ;  it  is  obtained  in  quantity  from  unripe  beans. 
It  differs  from  grape-sugar  in  not  affecting  polarized  light,  in  not  reducing 
metallic  oxides,  and  in  being  incapable  of  alcoholic  fermentation  ;  it,  however, 
yields  sarcolactic  acid  by  a  process  analogous  to  lactic  fermentation.  When 
a  solution  of  inosite  is  evaporated  with  nitric  acid  in  a  porcelain  capsule,  then 
moistened  with  calcic  chloride  solution  and  again  evaporated  after  the  addi- 
tion of  a  little  ammonia,  a  bright  rose-coloured  patch  remains  (Scherer's  test). 


32  NERVOUS    TISSUE. 

When  the  aqueous  extract  of  muscle  from  which  the  creatin  has  been  crys- 
taUized  out  (scy  Creatin)  is  precipitated  by  neutral  lead  acetate,  a  filtrate  is 
obtained  from  which  inosite  is  precipitated  by  the  addition  of  the  basic  acetate 
test.  It  crystallizes  from  its  solution  in  alcohol  in  rhombic  plates  or  prisms 
represented  by  the  formula  Cg  Hig  Og  +  2H2O. 

Creatin  (C4  H9  N3  Oj)  is  obtained  by  direct  crystallization  from  the  water- 
extract  of  meat.  To  prepare  it,  the  extract  must  be  first  freed  from  albumin 
by  boiling,  after  which  the  phosphates  and  sulphates  must  be  precipitated 
by  adding  to  the  strained  liquid  a  mixture  of  baryta  water  and  baric  nitrate. 
The  liquid  having  been  filtered,  the  filtrate  is  evaporated  over  a  water-bath 
to  a  small  bulk,  when  creatin  separates  in  hard  brilliant  crystals.  Creatin, 
when  treated  with  boiling  solution  of  baryta,  splits  into  Sarkosin  (Methyl- 
glycin)  and  Urea  (C4  Hg  N3  O^  +  H^  O  =  C3  H7  NOj  +  CO  (NHj)^). 
When  heated  with  acids,  it  loses  water,  and  is  converted  into  Creatinin 
(C,  H7  N3  O). 

Hypoxanthin  (C5  H^  N4  O)  (Sarkin  of  Strecker),  occurs  in  the  tissue  of 
the  spleen  and  in  muscle.  It  exists  in  the  mother  liquor  of  creatin,  and  can 
be  precipitated  from  it  as  an  impure  compound  '  of  argentic  nitrate  and 
hypoxanthin  by  treating  the  extract  with  solution  of  nitrate  of  silver  rendei'ed 
slightly  alkaline  by  ammonia.  Hypoxanthin,  like  xanthin,  is  soluble  in 
nitric  and  hydrochloric  acids  yielding  crystalline  compounds.  Heated  and 
evaporated  with  fuming  nitric  acid,  it  gives  the  same  yellow  residue  as 
xanthin. 

Xanthijt  (Cs  H4  N4  O3)  the  xanthic  oxide  of  Prout,  exists  in  extremely 
small  quantity  in  urine,  in  the  tissues  of  certain  organs,  and  as  an  occasional 
constituent  of  calculi.  It  is  very  insoluble  in  water,  but  soluble  in  hydro- 
chloric and  nitric  acids,  giving  crystallizable  compounds  with  both.  When  it 
is  heated  with  fuming  nitric  acid,  and  the  product  evaporated  to  dryness, 
a  pale  yellow  patch  is  left ;  from  this  circumstance  it  derives  its  name. 
Xanthin  can  be  prepared  artificially  by  the  action  of  oxidizing  agents  on 
Hypoxanthin. 

Nervous  Tissue. 

Of  the  proteids  of  the  brain  httle  is  known.  The  grey- 
substance  is  said  to  be  acid,  even  when  perfectly  fresh. 
All  nervous  tissue  contains,  in  addition  to  Cholcsterin  and 
Lecithin,  which  exist  everywhere,  a  body  called  Cercbrin, 
which  is  peculiar  to  the  nerve  fibres. 

Crystalline  Products  of  the  alcohol-ether  extract  of  Brain. 

Nctirin  or  Cholin  (N  (C  113)3  (C2  H.5  O)  OH)  is  a  strongly  basic,  colourless 
syrupy  fluid,  which  forms  crystalline  salts  with  acids.  It  is  soluble  in  alcohol 
and  water,  not  in  ether.  It  is  readily  decomposed  by  heat,  yielding  trimethy- 
lamine,  ethylene  oxide,  glycol  (C^  H4  (IIO)j)  and  water.     It  is  obtained  by 


EXCHANGE   OE    MATERIAL.  33 

heating  trimethylainine  ami  ethylene  oxide  in  aqueous  solution  (N  (C  ITOaH- 
C.J  II4  O  +  1I.J  O  =  Neurin).  Glyceio-phosphoiic  acid  (Cj  llg  PO^  or 
C3  Hj  O3  I'O  (01  It^),  the  product  which  is  obtained  when  phosphoric  anhy- 
dride or  glacial  phosphoric  acid  acts  on  glycerine,  is  a  syrupy  body,  soluble  in 
water  not  in  alcohol.  Taking  up  II^O,  it  splits  readily  when  warmed  into 
glycerine  and  phosphoric  acid.  Along  with  Neurin  and  a  fatty  acid,  it  is  a 
product  of  the  decomposition  of  Lecithin,  a  body  which  may  be  regarded  as 
glycero-phos])horic  acid  in  which  II^O  is  replaced  by  Neurin,  and  2  atoms  of 
H  in  the  radical  by  2  atoms  of  stearyl  (C,g  H^  O).  Lecithin  is  consequently 
called  Neurin-distearyl-glycero-phosphate.  Lecithin  is  an  imperfectly  crystal- 
lizable  body  which  fuses  readily,  is  soluble  in  ether  and  swells  out  in  water,  like 
starch,  without  dissolving.  It  is  obtained  by  treating  the  ether  alcohol 
extract  of  yolk  of  egg,  after  first  freeing  it  from  fats,  with  alcoholic  solution 
of  platinic  chloride.  A  chloride  of  platinum  and  of  Lecithin  separates,  of 
which  the  ethereal  solution,  when  decomposed  by  sulphuretted  hydrogen, 
yields  Lecithin  hydrochlorate  as  a  wax-like  mass.  The  alcoholic  solution  of 
this  substance,  when  poured  into  boiling  baryta  water,  splits  into  glycero- 
phosphate, Neurin  and  stearate.  Bodies  of  similar  constitution  in  which  the 
radical  of  stearic  acid  is  replaced  by  that  of  palmitic  or  of  oleic  acid  are  also 
called  Lecithins. 

ClioUstcrin  (Cjg  H44  O)  crystallizes  readily  from  ether-extract  of  powdered 
gall-stones  (of  which  it  is  usually  the  chief  constituent)  in  rhombic  plates, 
which  in  mass  have  a  mother-of-pearl  lustre.  These  crystals  contain  a  mol. 
of  II J  O,  which  they  lose  at  100°  C.  It  fuses  at  145°  C,  is  insoluble  in  water, 
soluble  in  alcohol,  ether,  chloroform,  &c.  When  evaporated  with  nitric  acid, 
the  residue  on  the  addition  of  ammonia  acquires  a  dull  red  colour.  If  sulphuric 
acid  is  added  to  its  volume  of  solution  of  cholesterin  in  chloroform,  the  solution 
becomes  first  red  then  purplish,  while  the  subjacent  layer  of  acid  acquires  a 
distinct  green  fluorescence.  A  body  resembling  Cholesterin  (Excretin)  has 
been  discovered  by  Marcet  in  human  foeces,  to  which  the  formula  C^,,  1X3^  O  is 
now  attributed. 

Cercbrin  is  a  body  of  imperfectly  known  constitution,  which  is  distinguished 
from  Lecithin  with  which  it  is  associated  by  its  solubility  in  boiling  alxsolute 
alcohol,  its  insolubility  in  cold  alcohol,  and  its  not  being  decomposed  or  acted 
upon  by  boiling  baryta  water. 


Exchange  of  Material. 

The  term  "exchange  of  material"  is  used  to  denote  the 
results  of  the  chemical  processes  ("functions"),  which  con- 
stitute the  life  of  the  animal  body,  as  they  exhibit  them- 
selves in  the  entrance  and  discharge  of  material  at  its 
surface.  Its  total  amount  is  known  by  the  direct  or 
indirect    measurement   of  the   quantities   of  carbon    and 

Ij 


34'  DISCHARGE   OF   CARBOX. 

nitrogen    discharged,  and   of  oxygen  taken  in  daily,  by 
the  organism,  when  the  body-weight  is  constant. 

The  Discharge  of  Carbon. 

The  influence  of  food  on  the  rate  of  discharge  of  COo  is 
direct  and  immediate.  The  increase  after  each  meal, 
which  may  amount  to  20  per  cent,  reaches  its  maximum 
in  about  2  hours.  The  effect  is  most  marked  when  the 
diet  consists  largely  of  carbohydrates. 

About  95  per  cent,  of  the  carbon  discharged  leaves  the 
organism  as  COg,  and  forms  part  of  the  "  insensible  loss," 
that  is,  the  loss  of  weight  of  the  body  when  no  food  is 
taken  and  no  liquid  or  solid  excreta  are  discharged.  The 
insensible  loss  is  made  up  of  the  sum  of  the  CO2  and 
water  discharged,  inhms  the  weight  of  oxygen  absorbed. 
In  man  it  amounts  to  about  25  grammes  per  hour. 

Of  the  total  hourly  discharge  of  CO,  less  than  half  per 
cent,  is  cutaneous.  The  hourly  discharge  of  CO2  by 
weight  of  an  adult  male  when  at  rest,  is  about  32  grammes, 
the  weight  of  oxygen  absorbed  in  the  same  time  being 
from  25  to  28  grammes.  The  hourly  discharge  of  water 
vapour  is  about  20  grammes. 

As  a  volume  of  COg  contains  the  same  weight  of  O  as 
an  equal  volume  of  O,  it  is  obvious  that  if  all  the  inspired 
O  were  discharged  as  CO^,  the  quotient  (by  volume) — called 
the  "Respiratory  Quotient" — -y-  would  be  =  i.  This, 
however,  is  never  the  case.  The  volume  of  O  absorbed 
exceeds  very  considerably  that  of  the  CO,  discharge,  the 
ratio  between  them  being  determined  by  the  composition 
of  the  food.  In  animals  which  feed  exclusively  upon 
carbohydrates,  equality  is  approached.  The  excess  of 
oxygen  is  greatest  when  the  diet  consists  largely  of  fats. 

On  a  mixed  diet  comprising  lOO  grammes  of  proteid,  100  grammes  of  fat, 
and  250  grammes  of  carbohydrates  [sec  Table  I.),  with  a  CO^  discharge  of 
770  grammes  daily,  the  assumption  of  O  by  the  organism  amounts  to  666 


DISCHARGE   OF   NITROGEN.  35 

grammes  daily,  of  which  560  grammes  are  discharged  as  COj,  about  9 
grammes  in  urea,  97  grammes  in  IIjO,  of  which  last  78  grammes  are 
formed  at  the  expense  of  the  hydrogen  of  the  fat.  Hence  the  quotient 
-,,— =  o'84.  In  inanition,  when  (as  in  the  case  represented  in  Table  II. 
the  proteids  and  fat  of  the  organism  take  the  place  of  food,  and  the  COj 
discharge  is  reduced  to  660  grammes  daily,  the  assumption  of  O  required  is 
649  grammes,  of  which  480  grammes  are  discharged  in  COj,  4*5  in  urea,  and 
l64'5  in  II3  O  ;  of  this  last  156  grammes  are  due  to  the  oxidation  of  fat. 

In  the  state  of  hibernation  the  respiratory  quotient  is 
smaller  than  in  any  other  known  condition  (often  less  than 
0*5),  for  the  hibernating  animal  lives  almost  entirely  on 
its  own  fat.  In  the  similar  state  of  inanition  the  excess 
of  the  oxygen  absorption  is  not  so  great,  for  here  the 
proteid  constituents  of  the  tissues  waste  in  much  larger 
proportion. 

The  "  insensible  loss  "  is  increased  by  muscular  work  ; 
for,  although  the  quantity  of  O  absorbed  is  large  during 
exertion,  this  is  far  more  than  counterbalanced  by  the 
greater  increase  of  the  COo  discharge  (diminution  of  the 
respiratory  quotient),  and  the  still  greater  augmentation 
of  the  evaporation  of  water  from  the  pulmonary  and  cuta- 
neous surfaces. 

Diminution  of  the  bodily  temperature,  however  pro- 
duced, determines  increased  CO.,  discharge.  In  small 
animals  the  CO.,  discharge  is  greater  in  proportion  to  the 
body-weight  than  in  large  ones. 

TJic  Discharge  of  Nitrogen. 

The  whole  of  the  nitrogen  which  enters  the  circulating 
blood  by  intestinal  absorption  (with  the  exception  of  so 
much  of  the  N  of  the  fasces  as  is  derived  from  unabsorbed 
secretions)  is  discharged  by  the  urine.  The  rate  of  dis- 
charge is  observed  to  vary  according  to  the  rate  at  which 
nitrogen  has  been  absorbed  during  the  previous  period,  so 
that  under  normal  conditions  the  processes  balance  each 
other.     But  in  order  to  the  establishment  of  this  state  of 

D  2 


36  ■  DISCHARGE   OF    NITROGEN. 

"  nitrog^en  equilibrium,"  it  is  necessary  that  the  daily  weight 
of  nitrogen  absorbed  should  not  fall  below  a  certain  limit, 
determinable  in  respect  of  each  species  of  animal  by  ex- 
periment. In  man  the  minimum  daily  allowance  of  N  is 
about  15  grammes,  or  0'02  per  cent,  of  the  body-weight; 
in  the  carnivora  about  O'l  per  cent.  ;  in  the  ox  0*005  per 
cent.  (Henneberg). 

When  the  diet  consists  of  proteid  exclusively,  a  larger 
quantity  is  required  for  the  maintenance  of  the  equi- 
librium than  when  it  also  ^contains  fat  or  carbohydrates. 
Accordingly,  in  those  animals  or  races  of  mankind  whose 
food  consists  largely  of  either  of  these  constituents — par- 
ticularly the  latter — the  nitrogen  requirement  is  lower  than 
in  others.     The  reason  why  this  is  so  is  not  understood. 

When  the  animal  body  is  deprived  of  food,  its  "  stored 
proteid "  rapidly  disappears.  During  this  process  (the 
first  stage  of  inanition,  and  which  lasts  a  few  days  only) 
the  nitrogen  discharge  as  rapidly  diminishes.  During  the 
second  stage  it  continues  to  diminish,  but  only  in  pro- 
portion to  the  diminution  of  the  total  body-weight. 

In  an  animal  fed  exclusively  with  flesh  the  nitrogen 
discharge  at  first  increases  pari  passu  with  the  absorption 
of  proteid,  the  absorption  of  O  being  increased  in  exact 
proportion  to  the  increase  which  has  taken  place  in  the 
quantity  of  material  to  be  disintegrated,  so  that  the 
respiratory  quotient  remains  nearly  unaltered  (Bidder  and 
Schmidt).  Although,  however,  the  overfed  animal  main- 
tains its  nitrogen  equilibrium,  it  usually  gains  weight,  and 
therefore  must  "  lay  on  "  fat. 

Relation  of  MiisaUar  Work  to  the  Discharge  of  Niti'Ogcn 
and  Carbon. — The  chemical  changes  on  which  the  per- 
formance of  work  by  muscle  depends,  manifest  themselves 
in  the  production  of  CO^  and  H^O.  Consequently,  in 
muscular  exertion  both  constituents  of  the  "insensible 
loss "  are  so  augmented  that  (irrespectively  of  the 
secondary  effect  produced    on   the  skin)   they  more  than 


c;ri.atine  and  iai'.  37 

bahuicc  llic  increased  absorption  of  ox}'gcn  (rcttcnkcjfer). 
The  quantity  pf  proteid  required  by  the  organism  daily  fcjr 
its  maintenance  is  proportional  to  the  weight  of  active 
living  material  (protoplasm)  that  it  contains,  so  that,  in 
general,  those  organisms  arc  most  vigorous  which  are 
capable  of  producing  the  largest  quantity  of  urea  in  pro- 
portion to  their  weight  ;  but,  in  the  case  of  muscle,  the 
proteid  so  used  is  not  the  source  of  the  work  done  ;  for 
even  if  the  whole  of  the  proteid  material  which  enters  the 
organism  in  a  day,  were  devoted  to  this  purpose,  and  em- 
ployed in  the  most  advantageous  way,  it  would  not  afford 
the  material  for  a  day's  work. 

The  facts  above  stated  are  most  easily  understood  on  the 
hypothesis  that  the  disintegration  of  food  proteid,  i.e.,  the 
production  of  urea  and  other  "nitrogenous  metabolites,"  is 
exclusively  a  function  of  "  living  material,"  and  that  this 
process  is  carried  on  in  the  organism  with  an  activity  which 
is  dependent  on  the  activity  of  the  living  substance  itself, 
and  on  the  quantity  of  material  supplied  to  it.  No 
evidence  at  present  exists  in  favour  of  a  "luxus  con- 
sumption "  of  proteid. 

Use  of  Gelatine. — In  carnivorous  animals  on  a  diet  of 
flesh  and  fat,  nitrogen  equilibrium  can  be  maintained  with 
a  much  smaller  daily  allowance  of  proteid  with  than  with- 
out gelatine.  Hence  gelatine  is  capable  of  partly  replacing 
proteid.  But  normal  nutrition  cannot  be  maintained  either 
with  gelatine  alone  or  with  any  mixture  of  gelatine  and 
fat,  or  of  gelatine  and  proteid. 

Relation  of  Fat  to  the  Exchange  of  Material. — Fat  is  stored 
for  the  purposes  of  nutrition  in  the  adipose  tissue,  which, 
without  any  disturbance  of  its  histological  integrity,  gives 
or  receives  fat  according  to  the  requirements  of  the  or- 
ganism. Tissue  fat  is  not,  however,  as  a  rule,  derived  from 
food  fat  of  the  same  kind,  for  even  when  animals  previously 
starved  receive  fatty  food,  the  fat  "  laid  on  "  is  not  neces- 
sarily chemically  identical  with  that  given.    In  the  fattening 


38  BALANCE   OF 

of  herbivorous  or  omnivorous  animals,  the  fat  is  largely 
produced  from  carbohydrates.  In  lean  carnivorous  animals 
it  is  deposited  when  they  are  well  fed  even  with  flesh 
without  fat.  Hence  it  must  be  concluded  that  in  such 
animals  the  formation  of  fat  from  proteids  is  a  normal 
process. 


TJie  Bala7ice  of  Income  and  Discharge. 

The  relation  between  the  income  and  expenditure  of  the 
animal  organism  is  best  expressed  in  the  form  of  balance 
sheets,  in  which  the  quantities  of  proteid,  fat  and  carbo- 
hydrates of  the  food,  are  stated  on  one  side,  and  COg,  urea, 
and  other  excreta  on  the  other,  the  value  of  each  item 
being  computed  according  to  the  weight  of  C  and  N  which 
it  contains.  The  income  and  discharge  of  H  are  left  out 
of  account  for  the  sake  of  simplicity. 

This  mode  of  statement  is  applicable  to  all  the  condi- 
tions of  nutrition  which  have  been  above  referred  to,  viz. 
(i)  that  in  which  the  quantity  and  quality  of  the  food  taken 
is  sufficient,  and  not  more  than  sufficient,  for  the  mainte- 
nance of  the  weight  of  the  body  without  loss  or  gain,  and 
in  which  the  diet  is  said  to  be  adequate  ;  (2)  the  condition 
of  inanition  in  which  the  body,  in  the  absence  of  food, 
nourishes  itself  at  its  own  expense ;  (3)  the  condition  in 
which,  in  the  absence  of  other  heat-producing  material, 
proteid  is  necessarily  employed  for  heat  production,  in 
larger  quantity  than  can  be  advantageously  disposed  of 
by  the  organism. 

These  three  cases  are  stated  in  the  following  Tables  : — 


INCOME  AND   DISCIIARGt. 


39 


TABLE  I.* 

Exchange  of  Material  on  Adequate  Diet. 

Income. 


Nitrogen 

Carbon. 

Albumin     . 

.   loo  grammes 

1 5  "5  grammes 

53 'o  grammes 

Fat    . 

.    lOO           ,, 

O'O          ,, 

790 

Carbohydrates 

•  250 

00 

93'0 

Urea 
Uric  acid 
Dejecta     . 

Respiration  (CO^) 


31-5  grammes) 
0-5        ..        ) 


15-5 
Expenditure. 

Nitrogen. 

1 4  "4  grammes 


O'O 

15  s 


225-0 

Carbon. 

6' 16  grammes 

10-84  M 

208-0        „ 


225-0 


The  quantities  of  albumin,  fat,  and  carbohydrates  in  the  Table  represent  a 
diet  consisting  chiefly  of  meat  and  bread,  with  the  addition  of  smaller 
quantities  of  potato,  butter,  and  eggs.  It  is  seen  that  in  man  the  discharge  of 
N  per  kilo,  of  body-weight  is  0-21  grammes,  and  of  carbon  3-03  grammes, 
the  quotient  -,  being  14-5.  In  the  carnivorous  animal,  which,  according  to 
Bidder  and  Schmidt,  uses  1-4  of  N,  and  6-2  of  C  per  kilo,  per  diem,  the  jt 
quotient  is  4-4.  In  the  human  being  on  a  flesh  diet,  the  exchange  of  N 
amounts  to  0-83  per  kilo,  per  diem,  and  the  j;t  quotient  is  5-2.  Thus  the 
exchange  of  material  of  the  human  organism,  when  fed  on  flesh,  is  interme- 
diate in  character  between  the  normal  exchange  and  that  of  the  carnivorous 
animal. 


TABLE  II. 
Exchange  of  Material  on  an  exclusively  Albuminous  Diet. 

Income. 


Food. 
Disintegration 


Nitrogen. 

62-3  grammes 


Carbon. 

279-6  grammes 
45 '9 


325-5 


•  The  data  on  which  Tables  I.,  II.,  and  III.  have  been  constructed  have 
been  derived  for  the  most  part  from  the  observations  of  Prof.  Ranke  on  him- 
self. 


40  INANITION. 


Outcome. 


Discharged  by  Excretion     44*3  grammes  263*0  grammes 

Retained  in  Store        .         i8'3        ,,  62*5        ,, 


62-3  325-5 

In  the  experiment  referred  to  in  this  Table  1832  grammes  of  meat  consumed 
as  food  yielded  3*4  per  cent,  of  Nitrogen,  i.e.,  62*3  grammes,  and  I2"5 
per  cent,  of  Carbon,  i.e.,  229*3  grammes.  Seventy  grammes  of  fat  also 
consumed  as  food  yielded  72  per  cent,  of  Carbon,  i.e.,  50*3  grammes: 
229*3  +  50*3  :=  279"6.  During  the  same  period  86'3  grammes  of  Urea  were 
discharged  daily,  containing  dfi'6  per  cent,  of  Nitrogen,  i.e.,  40*4  grammes, 
and  20  per  cent,  of  Carbon,  i.e.,  17 "3  grammes,  to  which  must  be  added  two 
grammes  of  Uric  Acid,  containing  33  per  cent,  of  Nitrogen,  i.e.,  o'66  gramme, 
and  35  per  cent,  of  Carbon,  i.e.,  07  gramme.  Further,  2*9  grammes  of  Nitro- 
gen and  14  grammes  of  Carbon  Avere  discharged  in  the  feeces,  and  231  grammes 
of  Carbon  were  expired  as  CO2.  Hence  the  total  discharge  of  Nitrogen 
(40'4  +  o"66  +  2'9)  was  43*96  grammes,  and  may  therefore  be  stated  as  44  : 
and  the  total  discharge  of  Carbon  (17  "3  -f  07  -f  14  +  231)  as  263  grammes. 
Deducting  the  quantity  of  Nitrogen  discharged  from  that  taken  in,  18  "3 
grammes  must  have  been  retained  in  108  grammes  of  Albumin,  and  conse- 
quently 53  per  cent,  of  that  weight  of  Carbon,  i.e.,  62*5  grammes. 

Comparing  the  quantity  of  Carbon  disposed  of  in  the  24  hours  with  the 
quantity  introduced  as  food,  we  find  that  the  latter  is  in  excess  by  45 '9 
grammes,  which  must  have  been  derived  from  the  disintegration  of  the  fat 
of  the  body. 

TABLE  III. 

Exchange  of  Material  in  Inanition. 
Disintegration  of  Tissue. 

Nitrogen.  Carbon. 

Albumin       .         .     50    grammes       7  "8  grammes         26 "5  grammes 
Fat      .         .         .   199-6        ,,  157-5 


184-0 


Discharge  of  Nitrogen  and  Carbon. 

Urea    .         .         .17     grammes  I     .,.0 

'     °  \    7  8  grammes  3  4  grammes 

Uric  Acid     .         .       0-2       .,         \     '      "^  ^^^ 

Respiration  (CO,)         .         .         .  i8o-6         ,, 


PRODUCTION   OF    HEAT.  4I 

This  Table  rejircsents  the  excliangc  for  a  twcnty-fDur  liour.-»'  period,  com- 
mencing twenty-four  hours  after  the  last  meal,  and  relating  to  the  same  person 
as  Table  I.  Thcr  discharge  of  N  per  kilo,  of  body-weight  was  reduced  to 
O'l,  »;■  being  2^'$.  In  the  carnivorous  animal,  in  prolonged  inanition,  the 
discharge  of  N  per  kilo,  is  0*9  per  diem  per  kilo,  and  ^  =.  6'6. 

In  fever  the  exchange  of  material  resembles  that  of 
inanition,  but  the  disintegration  of  proteid  is  more  rapid. 


TABLE   IV.  • 
Exchange  of  Material  in  Fcz'er. 
Disintegration  of  Tissue. 

Nitrogen.  Carbon. 

Albumin     .         .   120    grammes       i8"6  grammes  63 "6  grammes 

Fat    .         .         .   2057       „  157-4 


Discharge  of  Nitrogen  and  Carbon. 

Urea  and  Uric  Acid  40    grammes       iS'6  grammes  8*3  grammes 

Respiration  (CO.J  780         ,,  2127         ,, 


Production  of  Heat. 

Animal  heat,  like  mechanical  work,  is  a  result  of  the 
chemical  process  of  the  conversion  of  food  into  water, 
CO.,,  urea,  and  other  excreted  products. 

An  approach  to  an  experimental  proof  of  this  is  obtained 
by  comparing  the  quantity  of  heat  produced  by  a  man  or 
an  animal  in  a  given  time,  with  tiie  quantity  and  physio- 
logical "heat-value"  of  the  different  kinds  of  food  con- 
sumed during  the  same  period. 

Of  these  investigations  the  first  is  accomplished  calori- 
metrically ;    the  second    by  determining  the  quantity  of 

*  The  data  for  this  Table  are  to  be  found  in  a  paper  in  the  Practitioner 
for  April,  May,  and  June,   1S76. 


42  PRODUCTION    OF   HFiAT. 

heat  produced  by  each  substance  used  as  food  when  com- 
pletely burnt.  The  physiological  heat-value  of  any  sub- 
stance is  the  quantity  of  heat  produced  by  the  chemical 
disintegration  which  it  actually  undergoes  in  the  animal 
organism.  Those  substances  which  yield  in  the  living 
body  the  same  quantity  of  heat  as  by  complete  combus- 
tion in  the  laboratory,  have  the  same  physiological  as 
physical  heat-value ;  but  as  regards  substances  containing 
nitrogen,  the  result  must  be  corrected  by  deducting  from 
it  the  heat  produced  by  the  combustion  of  the  equivalent 
weight  of  urea.  Thus,  albumin,  which  by  complete  com- 
bustion yields  4998  units  of  heat,  has  a  physiological 
heat-value  of  only  4263  units.  The  results  so  obtained, 
although  only  approximately  correct  in  application,  are 
correct  in  principle ;  for,  however  various  may  be  the 
chemical  processes  of  animal  life,  their  value  as  regards 
the  quantities  of  heat  and  work  produced  must  be  esti- 
mated by  the  end-products. 

Of  the  heat  produced  in  the  body,  it  is  estimated  by 
Helmholtz  that  about  7  per  cent,  is  represented  by  ex- 
ternal mechanical  work,  and  that  of  the  remainder  about 
four-fifths  is  discharged  by  radiation  and  evaporation 
from  the  surface,  and  one-fifth  by  the  lungs  and  excreta. 

The  following  Table  exhibits  the  relation  between  the 
production  and  discharge  of  heat  in  twenty-four  hours  in 
the  human  organism  at  rest,  estimated  in  kilogramme 
units  or  calories  : — 


TABLE  V. 
Production  of  PIeat. 

Consumption  of  Albumin         .         (loogrms.)   .    100  X 4 "26^  =    426  Cals. 
,,  ,,    Fat         .         .         (loogrms.)    .    iooX^^=    907     ,, 

,,  ,,   Carbohydrates         {223gvms.)   .    223  X*^©  =1167     ,, 


PRODUCTION    OF    HEAT.  43 


Discharge  of  Heat. 

(1)  Warming  Water  in  Food.         .         .         .    2-6  kil(3.  x  25°  =       65-Cals. 

(2)  ,,        Air .         .         .         .  16  kilo.  X  25^  X  0-26  =     104     ,, 

(3)  Evaporation  in  Lungs       .....  630  at  58a  :=     367     ,, 

(4)  Radiation  and  Evaporation  at  Surface      .         .         .  /     .    =    1964    >i 

2500  Cals. 

The  mean  temperature  of  the  body  is  remarkably^con- 
stant,  but  is  higher  in  the  central  than  in  the  superficial 
parts.  The  uniformity  of  temperature  is  dependent  on 
the  constant  equilibrium  of  the  two  processes  by  which 
severally  heat  is  produced  and  discharged. 


44 


PRACTICAL    EXERCISES 


RELATING   TO   THE 


FOOD  STUFFS  AND  ANIMAL  LIQUIDS. 


I.— Starch,  Dextrin,  Dextrose,  Fat. 


1.  Starch,  is  insoluble  in  cold  water. 

2.  It  dissolves  imperfectly  in  hot  water  ;  the  liquid  so  obtained  is  opales- 
cent. 

3.  It  gives  a  blue  colour  with  iodine,  which  vanishes  when  the  liquid  is 
heated,  but  returns  on  cooling,  if  the  heating  has  not  been  prolonged. 

4.  Dextrin  is  soluble  in  water. 

5.  The  solution  gives  a  red  brown  colour  with  iodine,  which  vanishes  on 
heating. 

6.  Dextrose  (Grape-sugar)  is  crystalline  and  very  soluble  in  water. 

7.  It  reduces  many  metallic  oxides. 

8.  The  copper  test.  To  a  small  quantity  of  ten  per  cent,  solution  of 
cupric  sulphate  add  about  5  c.c.  of  the  liquid  to  be  tested  ;  then  solution  of 
caustic  potash  drop  by  drop  until  the  solution  is  clear,  and  heat  gradually.  If 
dextrose  is  present,  the  blue  colour  vanishes  and  a  yellow  precipitate  appears 
of  cuprous  hydrate,  or  a  red  precipitate  of  cuprous  oxide. 

9.  Conversion  of  starch  into  dextrose.  Boil  about  50  c.c.  of  starch  solution 
in  a  flask  with  a  drop  of  25  per  cent,  sulphuric  acid  for  five  minutes.  The 
liquid  becomes  limpid.  It  contains  in  addition  to  dextrose  much  unconverted 
soluble  starch. 

10.  Fat.  Lard  is  insoluble  in  water.  By  boiling  with  potash  it  yields  a 
solution  of  soap. 

11.  Decompose  the  solution  by  adding  a  few  drops  of  dilute  sulphuric  acid. 
On  heating,  a  layer  of  fatty  acid  collects  on  the  surface. 

12.  Microscopical  preparations.  Starch  grains  ;  their  disinte- 
gration by  hot  water ;  action  of  iodine  on  them.  Crystalline  forms  of  fatty 
acids. 

II.  — Milk,  Flow;  Bread. 

I.  Milk  has  (in  London)  usually  an  acid  reaction,  and  a  specific  gravity  of 
from   1025  to  1030.     After  removal  of  the  cream,  the  specific  gravity  is  higher. 


FOOD   STUFFS.  45 

2.  Milk  contains  fat,  sugar,  and  protoids. 

"•  Proteids.  Heat  about  50  c.c.  of  milk  in  a  fla^lk  to  50°  C,  add  two 
to  six  drojis  of  dilute  sulpluuic  aciil  (25  percent.)  and  shake  ;  the  milk  curdles  ; 
Strain  off  the  coagulated  casein  (curd)  through  muslin. 

I.  When  milk  is  _(illered  under  pressure  through  a  porous  disk,  its  casein, 
being  particulate,  remains  behind.  The  clear  fdtrate  contains  lactOSG 
(milk-sugar)  anil  salts. 

f.  The  strained  liquid  from  a  (whey)  contains  lactose,  which,  like  dextrose, 
reduces  metallic  oxides.     Apply  the  copper  test  (§  i,  S). 

d.  The  coagulated  casein  contains  much  fat  (butter)  which  can  be  extracted 
by  ether.     The  ether  extract  when  evaporated  on  paper  leaves  a  greasy  stain. 

f-  Butter.  Repeat  §  i,  lo  and  11.  Butter  yields  a  small  percentage  of 
volatile  acid. 

3.  Flour.      Wash  about  a  dessert-spoonful  of  sound  flour  in  a  muslin  bag. 
a.  A  milky  liquid  passes  through  containing  much  starch   (§  i,  3)  but  no 

swgar  (§  i,  8). 

h.  After  washing  for  some  minutes,  a  sticky  and  tenacious  material  remains 
on  the  muslin,  which  can  be  collected  ;  this  after  further  washing  forms  an 
elastic  mass  (gluten)  which  can  be  drawn  out  into  threads,  and  on  burning 
gives  off  the  smell  of  burnt  feathers  characteristic  of  a  proteid. 

4-  Bread.  Digest  with  warm  water.  The  extract  contains  starch  (§  i,  3) 
and  dextrose  (§  i,  8).     The  rcsichie  consists  principally  of  starch  and  gluten. 


III. — Albumin  and  its  Acid  and  Alkaline  Modifications. 

1.  Albumin.  WHiite  of  egg  (albumen)  when  diluted  with  water,  strained 
and  fdtered,  yields  a  .faintly  opalescent  liquid.  This  liquid  contains  a  proteid 
body,  albumin,  which  diffuses  through  an  animal  membrane  with  great 
difficulty  (§  ix,  8). 

2.  Such  a  liquid,  containing  five  per  cent,  of  albumen,  is  to  be  used  in  the 
following  experiments.     It  coagulates  on  heating  at  about  70"  C.  if  neutral. 

3.  To  some  of  the  liquid  add  a  few  drops  of  O'l  per  cent,  .solution  of  caustic 
potash,  and  warm  gently  for  two  or  three  minutes.  Boil.  The  liquid  w'ill  no 
longer  coagulate,  the  albumin  having  been  transformed  into  the  alkaline  modi- 
fication (alkali-albumin  or  casein). 

4.  In  a  similar  way  treat  another  portion  with  a  few  drops  of  very  dilute 
sulphuric  acid  (oT  per  cent.).  Warm  very  gently  for  not  less  than  five 
minutes.     On  boiling  no  coagulation  occurs,  the  albumin  having  passed  into 

its  acid  modification  (acid-albumin,  syntonin). 

5.  Cool  some  of  the  liquid  obtained  in  3.  Colour  it  with  litmus  solution, 
and  add  carefully  very  dilute  acid.  A  precipitate  falls  on  neutralization  which 
is  soluble  in  excess  of  acid. 

6.  Make  a  similar  experiment  with  the  liquid  obtained  in  4,  sulistitutinj 
weak  solution  of  potash  for  weak  acid.  A  similar  precipitate  occurs  on  neu- 
tralization, which  is  soluble  in  excess. 

7.  Take  three  portions,  of  5  c.c.  each,  of  the  original  liquid  in  three  test- 
tubes,  and  colour  them  with  litmus.     Dilute  the  o"i   per  cent,  acid  about  5 


4.6  GASTRIC  DIGESTION. 

limes,  and  add  a  drop  of  it  to  one  of  the  portions  ;  to  another  add  a  drop  of 
potash  solution  similarly  diluted.  Heat  all  three  tubes  gradually,  and  note 
the  temperature  at  which  each  coagulates. 

8.  Make  alkali-albumin  solution  as  in  3.  Divide  it  into  two  equal  parts. 
To  one  add  two  or  three  drops  of  ten  per  cent,  solution  of  sodic  phosphate. 
Colour  both  with  litmus  and  neutralize  with  weak  acid.  The  portion  without 
sodic  phosphate  is  precipitated.  The  other  portion  is  not  precipitated  until 
enough  acid  has  been  added  to  convert  the  sodic  phosphate  present  into  acid 
sodic  phosphate. 


IV. — Characteristics  of  Froteids.     Peptic  Digestion. 

1.  Tests  for  proteid  bodies  in  solution. 

a.  To  some  of  the  albuminous  liquid  referred  to  in  §  iii,  2,  add  strong 
nitric  acid.     The  precipitate  obtained  turns  yellow  on  boiling. 

/'.  Cool  the  liquid  in  a  and  add  strong  ammonia.     The  precijDitate  assumes 

an  orange  tint  (Xanthoprotein  reaction). 

c.  To  another  portion  add  MiUon's  reagent.  (Mercury  is  dissolved  in 
its  own  weight  of  strong  nitric  acid.  The  solution  so  obtained  is  diluted 
with  twice  its  volume  of  water.  The  decanted  clear  liquid  is  Millon's 
reagent.)     A  precipitate  is  formed  which  turns  dull  red  on  boiling. 

d.  To  a  third  portion  add  solution  of  potassic  ferrocyanide,  and  a  drop  of 
acetic  acid.     A  white  precipitate  appears. 

e.  Introduce  a  fourth  portion  of  the  liquid  into  a  test-tube  containing  one 
drop  of  ten  per  cent,  solution  of  cupric  sulphate.  On  adding  solution  of 
potash,  a  violet  colour  is  obtained  (compare  §  v,  2,  b). 

2.  Paraglobulin  (Fibrino-plastin). 

a.  Dilute  five  c.c.  of  serum  with  about  seventy-five  c.c.  of  water.  Neu- 
tralize carefully  with  a  few  drops  of  o-i  per  cent,  sulphuric  acid,  and  allow 
the  precipitate  to  settle. 

This  precipitate  is  soluble  in  excess. 

b.  Repeat  a,  passing  a  stream  of  CO,  through  the  liquid,  instead  of  neu- 
tralizing it  with  weak  acid. 

c.  Repeat  a  and  b  without  dilution.     No  precipitate  is  produced. 

3.  Peptic  Digestion. 

a.  Introduce  some  fibrin  into  a  test-tube  and  just  cover  it  with  0"2  per  cent. 
solution  of  HCl.  Allow  it  to  stand  for  forty-five  minutes  in  a  water-bath  at 
from  35"  to  38"  C.  At  the  end  of  this  time  the  fibrin  is  swollen  and  trans- 
parent, but  has  not  dissolved. 

b.  Repeat  a,  using,  instead  of  hydrochloric  acid,  water  to  which  a  drop  of 
glycerine  extract  of  pepsin  has  been  added. 

The  fibrin  remains  unaltered. 

c.  Repeat  a,  adding  a  drop  of  the  same  extract  to  the  acid  liquid.  The 
fibrin  dissolves  gradually. 

d.  Colour  with  litmus  the  liquid  obtained  in  c.  Neutralize  carefully  with 
weak  solution  of  caustic  potash  (§  iii,  6).  The  acid  albumin  formed  during  the 
first  stage  of  digestion  is  precipitated. 


rAN'CRKATIC   DIGESTIOX.  4J 


V. — Pancreatic  Dv^eslion.     Amylolytic  Ferments.     G ycogen. 

^    I.  Pancreatic  Digestion. 

a.  Introduce  fivac.c.  of  one  per  cent,  solution  of  sodium  carbonate,  to  which 
a  couple  of  drops  of  glycerine  extract  of  pancreas  have  been  added,  into  each 
of  two  test-tubes.  Boil  one  of  them  and  allow  it  to  cool.  Add  some  boiled 
fibrin  to  each,  and  place  them  both  in  the  water-balh  at  35'  C.  Compare 
the  changes  produced  with  those  observed  in  peptic  digestion  (§  iv,  3,  c). 

h.  Examine  the  liquid  product  of  a  pancreatic  digestion,  previously  pre- 
pared by  digesting  albumin  as  in  a.  It  is  alkaline,  and  may  have  a  charac- 
teristic and  offensive  odour. 

c.  Boil  some  of  this  liquid  after  acidulating  slightly.  Albumin  is  coa- 
gulated. 

d.  Colour  another  portion  with  litmus,  and  neutralize  carefully  (§  iii,  5) ; 
alkali-albumin  is  precipitated. 

e.  In  a  liquid  obtained  by  concentrating  the  product  above  referred  to,  after 
having  separated  the  greater  part  of  the  proteids  contained  in  it,  test  for 
Tyrosin  by  adding  Millon's  reagent  and  boiling.  The  presence  of  Tyrosin 
is  indicated  by  the  reddish  colour  assumed  by  the  liquid. 

/.  The  liquid  contains  LeUCin  in  a  crystalline  form. 

2.  Peptones.  A  solution  obtained  either  by  pancreatic  or  peptic 
digestion  can  be  used. 

a.  The  solution  yields  no  precipitate  either  by  boiling  or  by  neutralization. 

/'.   When  treated  as  in  §  iv,  i,  e,  it  gives  a  red  instead  of  a  violet  colour. 

The  liquid  product  of  the  slow  putrefaction  of  proteids  resembles  in 
most  respects  that  of  pancreatic  digestion.  To  the  latter,  the  presence  of 
septic  organisms  is  not  essential. 

3.  Amylolytic  Ferments.  Prepare  some  starch  solution  and 
ascertain  that  it  contains  no  dextrose,  §  i,  2  and  8.  To  another  portion  add 
saliva,  and  place  the  tube  containing  the  mixture  in  a  water-bath  at  from 
35°  to  38°  C.  After  a  short  time,  the  product  will  be  found  to  contain 
dextrose. 

4-  Glycogen. 

a.  To  an  extract  of  liver  (prepared  by  extracting  the  perfectly  fresh  organ 
with  boiling  water  after  washing)  add  a  solution  of  iodine  in  jjotassic  iodide. 
The  liquid  assumes  a  red  colour  identical  with  that  yielded  under  similar' 
circumstances  by  dextrine  (st-e  §  i,  5). 

b.  On  treating  a  slice  of  washed  liver,  hardened  in  alcohol,  with  iodine 
solution,  a  similar  colour  is  seen. 

c.  Repeat  3,  substituting  extract  of  liver  for  starch  paste,  using  the  same 
precautions. 

\l.—Bile. 

1.  Observe  colour  and  reaction.  The  bile  of  carnivora  is  brownish-red, 
that  of  herbivora  green.  Neutralize  and  boil  in  a  test-tube,  .Bile  does  not 
contain  albumin. 

2.  Acidify  bile  with  acetic  acid  ;  miicin  is  precipitated 


48  BILE. 

3.  Prepare  a  solution  of  synlonin  (§  iii,  4)  by  digesting  albumin  in  water 
containing  o'2  per  cent,  of  hydrochloric  acid.  On  the  addition  of  a  drop  of 
bile,  the  mixture  curdles  en  masse.  If  a  large  quantity  of  bile  be  added, 
little  or  no  precipitate  may  be  formed,  the  liquid  being  rendered  alkaline. 

4.  Boil  bile  with  twice  its  bulk  of  strong  hydrochloric  acid  for  five  minutes. 
The  bile  is  decomposed  into  bile-resin  (cholic  acid  with  colouring  matter) 
and  glycin  and  taurin,  the  two  last-mentioned  substances  remaining  in 
solution. 

5.  Pettenkofer's  Test  for  Cholic  acid.    Spread  a  drop  of  bile 

in  a  thin  film  on  a  white  porcelain  capsule.  Mix  with  a  drop  of  strong 
solution  of  cane-sugar.  Add  concentrated  sulphuric  acid  drop  by  drop,  and, 
if  necessary,  warm.     A  deep  purplish-red  colour  appears. 

6.  Repeat  the  test  with  an  alcoholic  solution  of  bilill.  The  same  colour 
is  produced. 

7.  Gmelin's  Test  for  the  colouring  matter.    Spread  a  drop  of 

bile  in  a  thin  film  on  a  white  porcelain  capsule.  Allow  a  drop  of  strong 
nitric  acid  to  fall  into  the  middle  of  the  film  and  observe  the  effect.  The 
drop  becomes  surrounded  by  rings  of  green,  blue,  red,  and  yellow,  in  the 
order  in  which  they  have  been  named.  Consequently  the  green,  which  is  first 
formed,  is  eventually  farthest  from  the  drop  of  acid.  If,  instead  of  allowing 
the  liquid  to  remain  undisturbed,  the  acid  be  mixed  with  the  bile,  the  liquid 
passes  through  the  same  tints  in  the  same  order. 

8.  Warm  a  little  nitric  acid  in  a  test-tube.  Incline  the  tube  and  pour  bile 
down  the  side,  so  as  to  form  a  layer  over  the  acid.  The  colours  appear  as  in 
7,  at  the  line  of  contact  of  the  two  liquids. 

9.  Cholesterin.  Extract  gall-stones  with  ether.  The  extract  yields, 
on  evaporation,  crystals  of  cholesterin,  which,  when  dropped  into  warm 
sulphuric  acid,  dissolve  with  a  red  colour.  The  residue,  insoluble  in  ether, 
consists  of  colouring  matter  and  mucin. 

10.  Acidify  10  c.c.  of  bile  in  a  flask  with  hydrochloric  acid  and  add  zinc. 
Nearly  close  the  flask  with  a  cork  to  which  acetate  of  lead  paper  is  attached. 
The  taurin  of  the  bile  is  decomposed,  HjS  being  formed,  which  blackens  the 
lead  paper. 

Vll.  —  Un>]e. 

1.  Observe  reaction  and  colour. 

2.  Determine  the  specific  gravity,  either  by  weighing  or  with  the  urino- 
meter.     Observe  the  effect  of  temperature. 

3.  Compare  fresh  with  stale  urine  as  regards  appearance,  smell,  and  re- 
action. 

4.  Sulphates.  Add  baric  chloride  after  acidifying  with  hydrochloric 
acid.     A  white  precipitate  of  baric  sulphate  is  formed. 

5.  Chlorides,  Add  argentic  nitrate  after  acidifying  with  nitric  acid.  A 
white  curdy  precipitate  of  argentic  chloride  is  produced. 

6.  Phosphates.  Adfl  ammonic  molybdate  to  urine  which  has  been 
mixed  with  half  its  volume  of  nitric  acid.  Boil.  A  yellow  crystalline  pre- 
cipitate falls. 


URINE.  49 

7.  Urea.  To  urine  evaporated  to  one-third,  add  a  drop  of  nitric  acid  in  a 
watch-glass.  Glistening  scales  of  urea  nitrate  are  abundantly  formed  in  the  liquid. 

8.  Uric  Acid.  To  a  hundred  c.c.  of  urine  add  5  c.c.  of  strong  hydro- 
chloric acid.  Allow  the  liquid  to  stand  for  forty-eight  hours.  Dark  red 
crystals  of  uric  acitl  separate  from  the  liciuid. 

9.  UrOChrome.  Precipitate  about  50  c.c.  with  lead  acetate  and  a  drop 
of  ammonia.  Filter.  The  filtrate  is  colourless.  Scrape  the  precipitate  from 
the  filter  paper  into  a  capsule.  Mix  with  a  few  drops  of  strong  sulphuric  acid 
and  .idd  to  the  pasty  mass  a  little  alcohol.  Filter.  The  yellow  filtrate  on 
boiling  with  excess  of  strong  sulphuric  acid  turns  black.  Dilute  the  acid 
liquid  with  a  large  quantity  of  water.  The  uromelanine  which  separates 
in  flocks  is  characterized  by  its  extreme  solubility  in  ammonia.  It  can  be 
precipitated  from  its  solution  in  ammonia  by  sulphuric  acid. 

10.  Indigo.  To  500  c.c.  of  urine  add  250  c.c.  of  pure  hydrochloric  acid. 
Allow  the  liquid  to  stand  twenty-four  hours.  A  coppery  scum  floats  on  the 
surface.  P"ilter.  Treat  the  filter  first  with  ammonia  to  extract  the  urome- 
lanine, secondly  with  cold  alcohol,  which  acquires  thereby  a  red  colour.  On 
boiling  the  residue  in  alcohol  a  blue  solution  is  obtained,  which  exhibits  the 
absorption  spectrum  of  indigo-blue. 

N.  B. — In  consequence  of  the  large  quantities  which  must  be  used,  this 
experiment  cannot  be  carried  out  by  each  student. 

VIII.  — I.   Quantitative   determination  of  Urea.     Urea 

(CO  NjH<)  when  decomposed  by  suitable  oxidizing  agents,  yields  COj,  HjO 
and  N.  The  most  convenient  reagent  for  eflecting  this  decomposition  is  an 
alkaline  solution  of  sodic  hypobromite.  The  CO3  is  absorbed  by  caustic  soda. 
The  nitrogen  which  is  disengaged  is  collected  and  measured  in  a  suitable 
apparatus.  Every  37*3  c.c.  of  nitrogen,  at  ordinary  pressure  and  temperature, 
corresponds  to  0"i  grm.  of  urea.  The  hypobromite  solution  is  prepared  by 
adding  25  c.c.  of  bromine  to  250  c.c.  of  a  solution  containing  100  grm.  of 
caustic  soda. 

a.  If  Russell  and  West's  apparatus  is  used,  measure  oft"  in  a 
pipette  5  c.c.  of  urine  and  introduce  carefully  into  the  bottom  of  the  "re- 
action-tube." Rinse  the  sides  of  the  tube  with  distilled  water  until  the  liquid 
reaches  the  constriction.  Plug  with  the  caoutchouc  stopper,  avoiding  the 
introduction  of  air.  Fill  up  the  tube  with  the  hypobromite  solution  and  half  fill 
the  trough  with  water.  Fill  the  measuring  tube  with  water  and  invert  it  in  the 
trough.  Lift  out  the  stopper,  and,  without  loss  of  time,  place  the  measuring 
tube  over  the  reaction-tube.  Warm  the  bulb  of  the  latter  until  the  liquid  just 
boils,  and  read  off  the  quantity  of  gas  collected. 

l>.  If  Dupre'S  apparatus  be  used,  introduce  25  c.c.  of  hypobromite 
into  the  flask  c.  Measure  off  5  c.c.  of  urine  into  the  test-tube,  and  close  the 
flask  with  the  caoutchouc  stopper  to  which  the  test-tube  is  attached.  Open 
the  pinch-cock  d  and  lower  the  measuring  tube  a,  until  the  surface  of  the  water 
is  at  the  zero  point  of  the  graduation.  Close  the  pinch-cock  and  raise  the 
measuring  tube.  If  the  apparatus  be  tight,  mix  the  urine  gradually  with  hypo- 
bromite solution  by  inclining  the  flask.  Finally,  tilt  the  flask  so  as  to  rinse  out 
the  test-tube  with  the  solution,  and  shake  well  for  a  few  seconds.     Immerse 

E 


50 


UREA. 


the  flask  in  a  vessel  containing  water  at  the  same  temperature  as  that  in  the  jar. 
At  the  same  time  lower  the  measuring  tube.  After  two  or  three  minutes, 
raise  the  measuring  tube  again  until  the  surfaces  of  the  liquids  inside  and  out 
coincide.  Read  off  the  quantity  of  nitrogen  which  results  from  the  de- 
composition of  the  5  c.c.  of  urine. 


DvI'RE's    L  Kfc 


The  stopper  and  test-tube  represented  in  the  upper  left  hand  of  the  figure  take  the  place 
of  the  stopper,  pipette  and  tube  e  f.     The  woodcut  has  been  kindly  lent  by  Dr.  Dupie. 

Phosphates.  When  solution  of  uranic  nitrate  or  acetate  is  added  in 
successive  quantities  to  a  hot  solution  containing  phosphates,  previously 
acidified  with  acetic  acid,  the  whole  of  the  uranium  is  precipitated  so  long  as 
any  phosphate  remains  in  solution  as  uranic  phosphate.     As  soon  as  an  excess 


PLASMA   AND  SERUM.  5  I 

of  uranic  salt  is  present,  it  can  be  detected  by  potassic  ferrocyanide,  which 
gives  a  brown  colour  with  uranic  salts. 

The  standard  uranic  nitrate  solution  contains  35  "5  grammes  in  a  litre.  One 
c.c.  corresponds  to  0005  gr.imme  PjOj. 

To  50  c.c.  of  urine  add  5  c.c.  of  a  solution  containing  loo  grammes  of  sodic 
acetate  in  900  c.c.  of  water,  to  which  100  c.c.  of  glacial  acetic  acid  have  been 
added.  Heat  the  55  c.c.  to  80°  C.  Add  the  uranic  nitrate  solution,  until  a 
drop  of  the  mi.xture  placed  on  a  white  porcelain  slab  gives  a  distinct  brown 
colour,  with  a  drop  of  potassic  ferrocyanide.  Note  the  quantity  of  solution 
used  and  calculate  therefrom  the  percentage  of  PjOi  in  the  urine.* 


IX. — Blood — Plasma  and  Serum. 

*,•   The  experiments  described  in  this  section  cannot  be  satisfactorily  carried  out  in  xvarm 

xueather. 

1.  Dilute  about  i  c.c.  of  sodic  sulphate  plasma  (obtained  by  collecting 
blood  in  one-third  of  its  volume  of  saturated  solution  of  sodic  sulphate)  with  20 
times  its  volume  of  water  and  place  in  a  water-bath  warmed  to  about  35°  C.  ;  it 
will  probably  coagulate  in  about  20  to  30  minutes. 

2.  To  a  second  similarly  diluted  liquid  add  a  drop  or  two  of  solution  of 
"blood-ferment  "  (prepared  by  precipitating  serum  with  alcohol,  collecting  the 
precipitate,  drying  in  vacuo  and  extracting  with  water).  The  addition  of  this 
solution  promotes  coagulation. 

3.  To  2-3  c.c.  of  pericardial  fluid  (from  the  horse)  or  hydrocele  liquid  add  a 
little  serum  and  place  the  mixture  in  a  warm  bath  ;   it  will  coagulate. 

4.  Saturate  about  5  c.c.  of  pericardial  fluid  with  sodic  chloride,  by  adding 
finely-powdered  salt,  and  shaking  ;  a  proteid  substance  separates  and  forms  a 
thick  scum  on  the  surface.  Pour  off  the  liquid,  dissolve  the  scum  in  water, 
add  a  few  drops  of  serum,  and  place  in  the  warm  bath  ;  the  mixture  will 
coagulate. 

5.  Precipitate  about  5  c.c.  of  sodic  sulphate  plasma  as  in  4,  dissolve  the 
sticky  precipitate  in  water  and  place  in  the  warm  bath  ;  the  solution  will 
coagulate. 

6.  Acidify  5-10  c.c.  of  serum  with  a  drop  of  acetic  acid  and  boil,  filter  off 
the  albumin  and  evaporate  the  residue.  Sodium  chloride  crystallizes  in  aggre- 
gations of  cubes.' 

7.  Dilute  I  part  of  serum  with  15  parts  of  water,  add  a  drop  or  two  of 
dilute  acid  (O'l  per  cent.).     Paraglobulin  is  precipitated  {see  §  iv,  2,  a). 

*  For  details  as  to  the  hypobromile  method,  see  Dupre's  original  paper  in 
the  Jottnial  of  the  Chemical  Society,  1877,  vol.  i.  p.  534. 

The  method  for  the  determination  of  PjOj  is  practised  in  this  class  as  an 
example  of  a  volumetric  process.  For  other  methods  relating  to  the  urine 
consult  Handbook  for  the  Physiological  Laboratory,  pp.  545-558.  It  is 
important  to  remember,  that  in  order  to  obtain  trustworthy  results,  as 
scrupulous  care  must  be  taken  in  the  measurement  and  collection  of  the  urine 
passed  during  the  period  of  observation  as  in  the  analytical  procedures. 

E    2 


52  COLOURING   MATTER 

AflBC  D  E-^F  G 


OF   IJLOOD.  53 

8.  Tie  up  in  a  piece  of  bladder  or  other  animal  membrane  some  whipped 
blood,  and  place  the  bag  containing  the  blood  in  a  beaker  of  distilled  water. 

The  colouring  matter  and  proteids  exhibit  but  a  slight  tendency  to  pass 
through  the  membrane  ;  the  soluble  salts  pass  through  readily,  and  their 
presence  can  be  xecognized  in  the  water  by  the  usual  tests. 

9.  Pour  over  some  fd)rin  contained  in  a  watch-glass  some  solution  of 
peroxide  of  hydrogen.  Bubbles  of  oxygen  are  given  off.  If  some  tincture  of 
guaiacum  be  added  a  blue  colour  is  developed.  Gluten,  potato  peelings,  and 
many  other  substances  develop  a  blue  colour  under  the  same  conditions. 


X.~T/u-  Colouring  Matter  of  the  Blood. 

1.  Observe  the  solar  spectrum,  noting  the  positions  of  the  dark  lines 
D,  E,  b  and  F,  in  relation  to  the  colours.  Compare  it  with  the  spectrum  of 
a  gas  flame,  which  shows  no  dark  lines. 

2.  Observe  the  spectrum  of  a  flame  coloured  with  sodic  chloride,  noting  the 
position  of  the  bright  yellow  line. 

3.  Oxy -haemoglobin,  introduce  defibrinated  blood  into  a  test-tube, 
and  observe  its  opacity  when  undiluted. 

a.  Dilute  by  adding  five  to  ten  times  its  bulk  of  water.  Place  the  test-tube 
in  front  of  the  slit  of  the  spectroscope,  direct  it  to  a  gas  flame.  The  only  light 
which  passes  through  is  that  of  the  red  end  of  the  spectrum. 

/'.  Add  water  until  the  green  appears.  Note  the  dark  space  (absorption 
band)  between  the  red  and  green. 

c.  Dilute  still  further  until  the  yellow-green  light  is  distinguishable  in  the 
middle  of  the  dark  space,  dividing  the  single  broad  band  into  two. 

d.  After  a  further  addition  of  water,  note  that  the  band  nearest  the  D  line 
is  somewhat  more  sharply  defined  than  the  other.  The  spectioim  is  still 
shortened  by  the  absorption  of  its  violet  end. 

e.  On  diluting,  until  the  solution  is  almost  colourless,  two  faint  bands  ar 
still  visible. 

f.  Map  on  the  diagram  the  appearances  observed  in  3,  h  and  d. 

4-  Reduced  Haemoglobin.  To  some  blood  diluted  as  in  3,  d,  add  a 
drop  of  solution  of  amnionic  sulphide,  and  warm  gently.  The  colour  becomes 
purjilish.  Place  the  tube  in  front  of  the  slit  as  before,  and  observe  the 
change  which  has  occurred.  A  single  absorption  band,  with  ill-defined  edges, 
takes  the  place  of  the  two  bands  previously  obsen-ed.  Map  its  position  on 
the  diagram. 

5-  Alkaline  Haematin.  Add  to  solution  of  blood,  rather  stronger 
than  the  last,  a  drop  of  solution  of  caustic  potash.  Warm  gently ;  the  colour 
completely  changes.  An  absorption  band  appears  to  the  left  of  the  line  D, 
and  much  of  the  blue  end  of  the  spectnim  is  cut  off. 

6.  Reduced  Alkaline  Haematin.  To  the  solution  obtained  in  5 
add  a  drop  or  two  of  anunonic  sulphide  and  warm  gently.  Observe  the 
change  of  colour.  Dilute  if  necessary.  A  strongly  marked  band  is  seen  to  the 
right  side  of  the  line  D,  and  a  second  less  defined,  which  nearly  coincides  with 
the  line  E. 


54  COLOURING   MATTER  OF   BLOOD. 

7.  CO-llSeillOglobill.  Blood  which  has  been  acted  upon  by  carbonic 
oxide  has  a  pecuUar  cherry-red  colour.  The  two  absorption  bands  have  nearly 
the  same  position  as  those  of  Oxy-hsemoglobin,  but  no  change  is  produced 
when  the  liquid  is  treated  with  reducing  agents,  as  in  4. 


Part  II. 

THE   MECHANICAL   PROCESSES. 

Muscular  Contraction. 

Muscle  consists  of  parallel  fibres,  each  of  which  is  a 
tube  containing  contractile  living  substance.  This  living 
substance  is  of  two  kinds,  which  differ  in  their  optical 
properties,  and  are  arranged  in  layers  alternating  with 
each  other.  In  contraction  their  absolute  and  relative 
volumes  alter.  So  long  as  the  tissue  is  living,  the  con- 
tractile substance  can  be  squeezed  out  as  juice  (muscle- 
plasma),  but  after  death  it  solidifies  and  exhibits  a  tendency 
to  split,  transversely  and  longitudinally.  Muscle  is  neutral 
when  living,  acid  after  death.  Muscle-plasma  coagulates 
spontaneously  at  all  temperatures  above  that  of  freezing. 
At  40°  C.  coagulation  is  instantaneous  :  the  promptitude 
with  which  it  occurs  is  the  less,  the  lower  the  temperature. 
The  coagulum  is  myosin  {see  p.  31). 

The  chemical  changes  which  constitute  the  life  of  muscle 
manifest  themselves  in  the  production  of  COg  and  HgO, 
which  are  disengaged  in  the  proportions  in  which  they 
result  from  the  combustion  of  carbohydrates.  When  the 
tissue  is  inactive,  these  are  formed  in  very  inconsiderable 
quantities  ;  but  in  muscular  activity,  the  rate  of  discharge 
is  increased  in  proportion  to  the  work  done. 

Living  muscle  is  elastic,  contractile  and  transparent. 
As  life  ceases  it  stiffens,  shortens,  loses  its  contractility 
and  transparency,  and  the  contents  of  its  fasciculi  become 
solid.  Death  of  muscle  is  promoted  by  defective  blood 
supply,    high   temperature   or   injury.       It    is    slow    and 


56  MUSCULAR   CONTRACTION. 

gradual  in  the  frog,  rapid  in  man  and  mammalia.  It  is 
associated  with  chemical  changes  which  resemble  those 
which  take  place  in  contraction. 

Partial  rigor  can  be  induced  in  living  muscle  by  arrest,  and  removed  by 
restitution,  of  the  circulation.  Muscle  becomes  rigid  at  about  45°  C.  in 
frogs,  48°  to  50°  in  mammals.  Rigor  occurs  sooner  after  death  in  exhausted 
muscles  than  in  others  :  all  rigid  muscles  are  acid. 

In  doing  work  muscle  shortens  and  thickens.  Its  vol- 
ume diminishes  very  slightly  and  it  becomes  more  exten- 
sible. Every  muscular  contraction  results  from  excitation 
either  extrinsic  or  intrinsic.  An  instantaneous  extrinsic 
excitation  of  a  muscle  by  its  nerve  produces  a  single 
contraction,  called  a  twitch.  The  contraction  begins  a 
certain  time  after  the  excitation  (period  of  latent  excita- 
tion of  du  Bois-Reymond) ;  it  rapidly  increases  to  a  maxi- 
mum and  then  gradually  subsides.  After  contraction 
has  ceased  the  muscle  is  nearly  as  long  as  before,  and 
soon  quite  as  long. 

By  the  myographic  method  {see  Practical  Exercises) 
a  single  contraction  may  be  investigated  with  reference  to 
the  time  after  excitation  at  which  it  begins,  to  its  duration 
and  character,  and  to  the  modifications  produced  by 
changes  in  its  physiological  condition,  or  in  its  temperature. 
If  two  or  more  instantaneous  excitations  of  a  muscle 
through  its  nerve  follow  each  other,  the  effect  is  augmented 
by  each  successive  excitation ;  but  the  increment  produced 
by  any  single  excitation  is  always  less  than  that  produced 
by  its  predecessor.  The  effect  of  a  series  of  equal  exci- 
tations following  each  other  at  very  short  intervals  of 
time,  although  apparently  continuous,  consists  in  reality 
of  a  succession  of  instantaneous  contractions,  of  which 
the  frequency  is  the  same  as  that  of  the  excitations.  This 
condition  is  called,  in  physiological  language.  Tetanus. 
The  number  of  single  contractions  per  second  of  which  a 
tetanic  or  voluntary  contraction  is  constituted  may  be 
judged  of  by  the  "  tone"  heard  in  the  contracting  muscle. 


MUSCULAR   CONTRACTION.  $7 

In  ordinary  voluntary  contraction  in  man,  the  tone  has  a 
vibration  rate  of  from  38  to  40  per  second. 

Under  the  influence  of  the  arrow  poison  (curare),  the 
end-organs  of  the  muscular  nerves  become  incapable  of 
performing  their  function,  so  that  the  muscles  of  animals 
poisoned  by  this  drug  are  virtually  nerveless.  The  con- 
traction produced  by  instantaneous  excitation,  at  any 
point  of  a  "  curarized  "  and  extended  muscle,  progresses 
from  the  point  excited  in  the  direction  of  the  fibres.  In 
fresh  muscles  the  rate  of  progress  of  the  contraction  wave 
is  from  3  to  4  metres  per  second  ;  the  duration  of  the 
contraction  is  about  O'O/  second  ;  hence  the  wave  length  of 
contraction  is  about  a  quarter  of  a  metre.  In  exhausted 
muscles  and  in  muscles  under  the  influence  of  cold,  the 
rate  of  progress  is  slower  than  in  fresh  muscle  at  the 
ordinary  temperature. 

The  above  statements  refer  to  the  effects  of  single  induction  shocks,  or  of 
successions  of  them.  If  a  voltaic  current  is  led  for  a  moment  through  a 
curarized  muscle,  the  tissue  is  excited  at  the  negative  pole  (cathode)  at  the 
closure,  and  at  the  positive  pole  (anode)  at  the  opening  of  the  circuit.  In 
this  case,  the  muscle  remains  contracted  during  the  whole  period  that  the 
current  is  passing. 

By  the  term  "absolute  force"  is  denoted  the  heaviest 
weight  a  muscle  is  able  Just  to  lift,  when  contracting  to 
the  utmost  advantage  under  the  influence  of  a  sufficient 
excitation.  The  weight  which  a  muscle  is  able  to  lift 
varies  according  to  its  extension,  being  greatest  when  it  is 
most  extended — consequently  greater  at  the  beginning  of 
a  tetanic  or  voluntary  contraction  than  at  the  end.  The 
maximum  quantity  of  work  is  done  by  a  muscle  when  it 
is  nearly  loaded  to  the  utmost  throughout  the  whole  con- 
traction. In  order  that  this  may  be  the  case,  the  load  and 
the  power  of  the  muscle  to  lift  it  must  diminish  at  the  same 
rate.  If  the  load  to  be  lifted  remains  constant,  the  muscle 
acts  most  advantageously  {i.e.  does  most  work)  when  the 


58  MUSCULAR   CONTRACTION. 

weight  is  considerably  less  than  the  maximum  weight 
which  the  muscle  is  able  to  lift.  Muscle  is  elastic :  a 
muscle  extended  by  a  load  recovers  its  original  length 
when  the  load  is  removed.  When  a  loaded  muscle  is 
extended  by  successive  additions  of  equal  weights  to  its 
load,  the  increase  of  length,  resulting  from  each  addition, 
becomes  less  and  less  as  the  extension  proceeds,  until  no 
further  increase  is  observable.  Of  two  muscles,  of  which 
one  is  in  tetanus,  the  other  at  rest,  the  former  is  more 
extended  by  the  same  weight  than  the  latter. 

In  contraction  the  temperature  of  muscle  is  slightly 
raised  :  the  greater  the  effort,  and  the  less  the  work  done, 
the  greater  the  rise. 

In  living  muscles,  differences  of  electrical  tension  are 
usually  observed  between  different  parts  of  the  natural 
surface,  which  differences  can  be  shown  to  be  intimately 
associated  with  the  vital  properties  of  the  tissue,  and 
cease  with  the  cessation  of  its  life.  The  greatest  differ- 
ences (often  amounting  to  several  hundredths  of  a  Volt) 
present  themselves  when  a  sound  surface  is  compared 
with  an  injured  one,  the  injured  part  being  always 
negative  to  the  sound.  In  a  muscle  which  is  at  rest, 
all  parts  being  in  the  same  physiological  condition,  the 
surface  is  (according  to  Hermann)  isoelectric  or  equi- 
potential.  Such  a  condition  is  rarely  met  with  in  the 
voluntary  muscles,  for  the  slightest  exposure  or  injury 
produces  electrical  inequality,  but  is  easily  observed  in 
the  resting  heart.  In  voluntary  muscles,  separated  from 
the  body,  it  is  commonly  observed  that  the  end  surfaces 
are  negative  to  the  lateral  surfaces.  During  the  state 
of  excitation,  which  precedes  contraction  (period  of 
latent  excitation)  the  electrical  state  of  (uninjured)  mus- 
cular tissue  undergoes  a  change  which  consists  in  its 
becoming  negative  to  the  unexcited  parts.  In  tetanus 
this  change  precedes  each  single  contraction  {see  p.  56). 
In    nerveless    (curarized)     muscles,    the    excitatory    state 


CIRCULATION.  59 

is  propagated  along  the  fibres  at  a  rate  which  agrees 
with  that  of  the  propagation  of  the  wave  of  contraction, 
so  that  the  latter  is  preceded  in  its  progress  by  the 
former.  In  ntrved  tnuscles,  which  are  excited  through 
their  nerves,  the  excitatory  waves  are  similarly  propa- 
gated, but  originate  from  nerve  endings.  In  injured 
muscle  the  electrical  difference  between  injured  and 
uninjured  surfaces  is  diminished  during  excitation. 
This  excitatory  effect  was  therefore  called  by  du  Bois- 
Reymond  the  "  negative  variation." 

The  excitatory  disturbance  is,  in  all  cases,  followed  by 
other  changes,  which  correspond  in  time  to  the  contrac- 
tion, but  have  not  yet  been  fully  investigated. 

All  of  the  phenomena  above  described  are  comprised  by  du  Bois-Reymond 
in  a  theory,  according  to  which  every  portion  of  living  muscular  fibre  con- 
tains electromotive  particles,  each  of  which  has  ends  (poles),  which  are 
directed  towards  the  ends  of  the  fibre,  and  are  negative  to  the  zonal  surface, 
which  corresponds  to  the  surface  of  the  fibre.  The  effect  of  excitation  is 
to  produce  a  momentary  diminution  of  the  electromotive  force  of  these 
particles.  The  particles  being  called  by  du  Bois-Reymond  *  molecules, '  the 
theory  is  known  as  the  molecular  theory  of  the  muscle  current. 

In  involuntary  muscle  the  process  of  contraction  is 
similar,  but  much  slower.  It  is  attended  with  electrical 
changes  of  the  same  nature  as  those  observed  in  volun- 
tary muscle. 


Circulation. 

TJie  Arterial  Circulation. — The  arterial  system  is  an 
elastic  receptacle  for  blood,  the  form  of  which  is  dendritic. 
At  the  ends  of  the  ramifications,  blood  flows  by  in- 
numerable capillary  channels  into  the  venous  system. 
Into  the  trunk,  blood  is  injected  at  intervals  by  the 
heart,  each  injection  lasting  from  three  to  four-tenths  of 
a  second.  In  the  aorta  the  blood  is  squeezed  by  the 
arterial    wall    with  pressures  which  probably   vary   from 


6o  CIRCULATION. 

6  to  10  inches  (=  150  to  250  millimeters)  of  mercury 
=  ^  to  -g-  of  an  atmosphere  =r  3  to  5  lbs.  on  the  square 
inch.  It  is  this  pressure  which  is  the  cause  of  the  cir- 
culation. Its  maintenance  is  the  function  of  the  heart. 
The  sum  of  the  limiina  of  the  capillaries  is  much  greater 
than  that  of  the  aorta :  the  velocity  of  the  capillary 
blood-stream  is  in  the  same  proportion  less.  Arterial 
tissue  recovers  its  length  after  stretching  as  perfectly  as 
muscle  :  it  is  however  more  extensible.  In  the  living 
body,  its  elastic  properties  are  modified  according  to  the 
degree  of  contraction  of  the  muscular  elements  it  con- 
tains. 

The  arterial  blood-stream  can  be  best  understood  by 
reference  to  the  schemata  described  below. 

Schema  i.  As  regards  the  relation  of  pressure  to  pro- 
gressive motion,  the  arterial  system  is  represented  by  a 
tall  cylindrical  bottle  from  the  bottom  of  which  water 
flows  through  a  horizontal  tube  of  equal  width  through- 
out. In  the  arterial  system,  as  in  the  schema,  the  lateral 
pressure  (supposing  the  velocity  of  the  blood-stream  to 
be  constant)  is  proportional  to  the  sum  of  the  resistances 
in  front.  If  such  a  bottle,  having  an  aperture  equal  to  the 
lumen  of  the  aorta,  were  substituted  for  the  heart, 
the  height  to  which  it  would  be  necessary  to  fill  it  with 
blood  in  order  to  carry  on  the  circulation  at  the  normal 
rate,  would  represent  the  force  required  for  that  purpose. 
That  height  multiplied  by  the  weight  of  blood  discharged 
per  second  in  grammes,  would  give  in  gramme-meters  the 
work  done  by  the  heart  in  the  same  time  in  maintaining 
the  circulation. 

Schema  2.  As  regards  wave  motion,  or  pulsation,  it  is 
represented  by  an  elastic  tube,  ab,  closed  at  both  ends 
and  moderately  distended  with  liquid,  into  which  water  is 
suddenly  and  for  a  short  time  injected.  The  phenomena 
observed  remain  unaltered,  if,  instead  of  closing  the  tube 
at  its  ends,  we  imitate  the  conditions  of  the  circulation  by 


CIRCULATION.  6l 

injecting  liquid  into  it  at  short  intervals  at  a,  allowing  it 
to  flow  out  by  a  small  opening  at  b.  In  the  arterial  system, 
just  as  in  this  schema,  the  momentary  distension  produced 
in  the  aorta  by  each  injection  of  blood,  is  propagated  to 
other  parts  of  the  system  at  a  rate  which  is  dependent 
on  the  previously  existing  pressure.  Every  such  sudden 
distension  is  followed  sooner  or  later  by  a  second,  which 
is  called  the  second  beat. 

By  virtue  of  the  elasticity  of  the  arteries,  part  of  the 
motion  which  is  communicated  to  the  blood  during  each 
ventricular  systole  is  stored  as  arterial  distension,  to  re- 
appear as  progressive  motion  during  the  diastolic  interval. 
If  the  arteries  were  not  elastic,  this  motion  would  lose 
itself  in  the  shock  of  the  blood  against  the  rigid  arterial 
wall,  whereby  the  arteries  would  be  injuriously  strained  at 
each  injection  of  blood,  and  the  effect  of  the  heart's  action 
would  be  diminished. 

Investigation  of  Arterial  Pressure. — The  haemadynamo- 
meter  is  a  mercurial  manometer  of  which  one  limb  can  be 
connected  with  an  artery  by  a  tube  containing  solution  of 
sodic  bicarbonate.  In  order  that  the  measurement  may  be 
accurate,  it  is  necessary  (i)  that  the  mean  level  of  the 
mercury  surface  in  the  proximal  limb  should  be  the  same 
as  that  of  the  arterial  aperture  ;  and  (2)  that  the  tube 
should  enter  the  artery  at  right  angles  to  its  axis. 

Any  instrument  by  which  the  arterial  pressure  can  be 
measured,  by  inscribing  its  variations  on  a  surface  moving 
horizontally  by  clockwork  at  a  uniform  rate,  is  called  a 
kymograph.  A  mercurial  kymograph  consists  of  three 
parts — the  clockwork  and  recording  cylinder  ;  the  mano- 
meter and  writer ;  the  tube  and  cannula  by  which  the 
manometer  is  connected  with  the  artery.  Its  uses  are 
(i)  to  measure  the  mean  arterial  pressure  and  to  record  its 
variations  ;  (2)  to  measure  the  duration  of  the  pulsation 
intervals.  Its  chief  defect  arises  from  the  "proper 
motion  "  of  the  mercurial  column.     The  spring  kymograph 


62  CIRCULATION. 

on  Bourdon's  principle  is  nearly  free  from  "  proper  motion," 
and  consequently  enables  us  to  measure  the  fine  variations 
of  arterial  pressure  in  the  course  of  each  pulse  interval. 

The  pulse  as  felt  by  the  finger  indicates  the  moment  of 
greatest  distension,  i.e.  that  of  greatest  pressure  in  the 
artery.  The  distinctness  with  which  it  is  felt  is  propor- 
tional to  the  shock  communicated  to  the  arteries  by  the 
heart.  Pulses  are  classified  according  to  frequency,  hard- 
ness, duration  and  dicrotism.  All  of  these  characters  may 
be  appreciated  by  the  finger,  but  are  studied  more  accu- 
rately by  the  sphygmograph. 

Three  events  may  be  distinguished  in  every  pulse,  viz., 
the  beginning  of  the  expansion,  the  collapse,  and  the 
beginning  of  the  second  beat.  Of  these  the  first  occurs 
in  the  normal  radial  pulse  about  0*15  second  after  the 
beginning  of  the  effective  part  of  the  systole  of  the  left 
ventricle.  The  second  is  synchronous  with  the  end  of 
the  systole,  and  hence  immediately  precedes  the  closure 
of  the  sigmoid  valves.  The  third  is  synchronous  with,  or 
immediately  after,  the  closure  of  the  valves. 

The  graphical  characters  of  the  arterial  pulse,  e.g.  the 
radial,  are  determined  by  {a)  the  character  of  the  diastolic 
notch  which,  in  the  tracing,  separates  the  first  from  the 
second  ascent,  and  {b)  the  relative  height  of  the  second 
ascent.  The  notch  is  produced  by  the  sudden  cessation  of 
the  flow  of  blood  from  the  ventricle  into  the  aorta.  It 
may  be  generally  stated  that  the  shorter  the  duration  of 
the  systole  and  the  less  the  vascular  resistance,  the  deeper 
is  the  notch. 

The  second  beat  is  determined  entirely  by  events  which  occur  in  the  arteries 
and  capillaries.  When  any  part  of  an  arteiy  is  suddenly  distended,  all  parts 
of  the  arterial  tree  beyond  pulsate  after  it ;  but  each  pulsates  at  a  different 
moment,  according  to  its  distance  from  the  par*  primarily  distended,  and  as 
each  attains  its  maximum  of  distension,  it  sends  back  a  return  wave  of  expan- 
sion. The  moment  at  which  the  strongest  return  waves,  and  the  greatest 
number  of  them,  arrive  at  the  point  of  observation,  is  that  at  which  the  second 
beat  occurs. 


CIRCULATION.  6^ 

Unnatural  frequency  of  pulse  depends  either  on  func- 
tional disturbance  of  the  cerebro-spinal  centres  or  increased 
bodily  temperature  (pyrexia).  Unnatural  cclcrily  of  pulse, 
i.e.  diminished  duration  of  the  period  of  expansion,  is  ob- 
served either  in  association  with  increased  frequency,  or 
in  consequence  of  mechanical  defect  of  the  aortic  valve. 
The  opposite  condition  (tardiness  of  pulse)  occurs  in 
advanced  age,  and  in  collapse  {e.g.  in  concussion),  or  under 
the  influence  of  certain  drugs,  particularly  of  opium  and 
digitalis. 

Velocity  of  the  Circulation. — The  velocity  of  the  blood- 
stream is  dependent  on  the  relation  of  the  effort  made  by 
the  heart  to  the  resistance  to  be  overcome  in  the  vessels. 
This  resistance  varies  according  to  the  condition  of  the 
vascular  nervous  system. 

It  is  believed  that  the  velocity  of  the  blood-stream  in 
the  aorta  is  about  a  foot  in  a  second  ;  in  the  capillaries 
about  I -50th  of  an  inch  ;  and  that  the  circulation  is 
accomplished  in  the  time  occupied  by  about  thirty  pulsa- 
tions of  the  heart. 

Of  the  instruments  used  for  investigating  the  progressive 
movement  of  blood  in  the  arteries,  those  by  which  the 
quantity  conveyed  in  a  given  time  can  be  estimated  are 
called  Dromometers  (e.g.  Volkmann's  and  Ludwig's),  those 
by  which  the  rate  of  movement  only  is  determined,  Tacho- 
meters. By  the  latter  we  learn  that  in  the  large  arteries 
the  second  beat  or  expansion  is  attended  by  a  cessation  or 
even  reversal  of  the  blood-stream  ;  by  the  former,  that  the 
rate  at  which  blood  is  transmitted  through  an  artery  is 
subject  to  great  and  often  sudden  variations,  and  that 
these  variations  are  independent  of  the  rate  at  which  blood 
is  discharged  into  the  arterial  system  by  the  heart. 

Capillary  Cireiilation. — In  studying  the  circulation  in  the 
transparent  parts  of  animals,  we  observe  that  the  smallest 
arteries  are  subject  to  great  variations  of  diameter,  and 
often  contract  rhythmically  ;  that  the  progressive  move- 


64  CIRCULATION. 

ment  in  arterioles  is  more  rapid  than  in  veins  of  corre- 
sponding size  ;  that  in  the  veins  the  coloured  corpuscles  are 
carried  along  by  the  axial  stream,  the  leucocytes  tending 
towards  the  vascular  wall ;  that  when  a  tissue  is  injured 
the  capillaries  begin  first  to  widen  and  then  to  leak,  the 
plasma  and  leucocytes  passing  out  in  succession,  and  that 
more  intense  injury  produces  stasis  and  extravasation  of 
the  coloured  disks. 

Circulation  in  the  Liver,  Kidneys,  and  Spleen. — The  dif- 
ference between  the  pressure  which  exists  in  the  trunk  of 
the  portal  vein  and  that  of  the  hepatic  vein  probably  does 
not  exceed  half  an  inch.  Consequently  the  blood-stream 
through  the  liver  is  extremely  slow.  In  the  kidneys,  the 
blood  enters  the  glomeruli  at  high  pressure  and  with  rapid 
motion  ;  in  the  capillaries  of  the  convoluted  tubes  the 
motion  is  slow,  and  the  pressure  that  of  the  venous  system. 
In  the  spleen,  the  quantity  of  blood  contained  in  the 
organ  at  one  time,  and,  consequently,  its  bulk  are  subject 
to  very  great  variations ;  these  are  mainly  due  to  the 
action  of  the  muscular  fibres  contained  in  the  capsule  and 
framework. 

Venous  Circtilation. — The  capacity  of  the  venous  system 
much  exceeds  that  of  the  arterial,  and  is  sufficient  for  the 
reception  of  the  whole  of  the  circulating  blood.  The  mean 
lateral  pressure  in  the  venous  system,  though  much  inferior 
to  that  which  exists  in  the  arteries,  is  dependent  on  it  and 
varies  with  it.  It  is  greater  in  the  capillary  veins  than  in 
the  venous  trunks  :  this  difference  is  the  chief  cause  of  the 
venous  blood-stream.  It  is  greater  during  inspiration  than 
during  expiration.  This  difference  is  more  marked  in  the 
intra-thoracic  veins  (where  during  inspiration  the  lateral 
pressure  sinks  below  that  of  the  atmosphere)  than  in  others  : 
it  manifests  itself  in  the  respiratory  movements  of  the  brain, 
and  other  similar  phenomena.  The  venous  blood-stream 
is  promoted  by  intermittent  external  pressure,  hindered  by 
continuous  pressure.      The  venous  pressure,    and,  conse- 


CIRCULATION.  6$ 

quently,  the  quantity  of  blood  in  a  limb,  and  the  velocity 
of  the  venous  blood-stream,  arc  much  influenced  by  posi- 
tion ;  but  this  docs  not  affect  the  quantity  of  blood  trans- 
mitted through  the  part  in  a  given  time.  A  slight  dimi- 
nution of  the  pressure  in  the  veins  nearest  to  the  heart 
accompanies  each  pulsation  :  this  is  due  to  the  diminution 
of  the  volume  of  the  heart,  which  occurs  at  the  moment  of 
ventricular  systole.  When,  from  disease,  the  tricuspid 
valve  is  incompetent,  the  opposite  effect  is  produced,  and 
is  called  the  venous  pulse. 

Veins  are  contractile,  but  there  is  no  proof  that  their 
contractility  is  of  physiological  importance  in  man.  In 
certain  animals,  the  veins  contract  rhythmically. 

The  LympJi-Strcam. — The  progressive  motion  of  the 
lymph  is  dependent  on  the  difference  between  the  pressure 
under  which  liquid  exudes  from  the  capillaries  into  the 
tissue  interstices  from  which  the  lymphatics  spring,  and 
the  pressure  which  exists  in  the  lymphatic  trunks.  In  all 
muscular  parts  it  is  promoted  by  the  alternate  tension  and 
relaxation  of  the  tendons  and  aponeuroses.  In  the  visceral 
cavities  it  is  similarly  aided  by  the  respiratory  variations 
of  external  pressure  to  which  the  trunks  are  subjected,  as 
well  as  by  the  circumstance  that  the  mean  pressure  in  the 
abdomen  is  greater  than  in  the  thorax.  Solid  particles, 
if  of  sufficient  minuteness,  whether  introduced  into  the 
blood-stream  or  into  the  tissues,  find  their  way  into  the 
lymphatics,  which  can  usually  be  "  injected  "  by  the  intro- 
duction of  any  particulate  liquid  into  living  tissue.  It  is 
probable  that  such  particles  are  for  the  most  part  arrested 
in  the  lymph  glands.  The  particulate  constituents  of 
chyme  are  forwarded  from  the  intestinal  cavity  into  that 
of  the  lacteals  by  the  agency  of  the  living  protoplasm  of 
the  epithelium  and  mucosa.  The  further  progress  of  the 
chyle  in  the  mesentery  is  promoted  by  muscular  action. 


^6  THE   HEART. 


The  Heart. 

The  heart  consists,  in  its  simplest  form,  of  a  muscular 
dilatation  provided  with  a  valve  or  valves  at  either  open- 
ing, and  a  venous  antechamber  or  reservoir,  which  in 
the  lower  vertebrates  is  more  perfect  than  in  man  and 
mammalia.  In  the  osseous  fishes  another  dilatation 
(the  bulbus  arteriosus)  exists  between  the  ventricle  and 
the  branchial  arteries,  the  function  of  which  is  to  store  up 
energy  during  the  ventricular  systole,  as  the  arteries  do 
in  mammals.  In  the  cartilaginous  fishes  the  bulb  is  a 
muscular  organ  in  which  energy  originates,  and  it  is  often 
provided  with  valves.  These  compHcations  in  the  struc- 
ture of  the  central  organ  are  rendered  necessary  by  the 
simplicity  of  the  circulation.  In  the  batrachians  the  bulb 
is  less  required,  for  only  part  of  the  blood-stream  passes 
through  the  respiratory  apparatus,  but  the  auricles  are 
still  provided  with  valves.  In  the  mammalian  heart,  the 
mechanism  of  respiration  renders  the  auricular  valves 
unnecessary. 

Motions  of  the  Heart  and  phenomena  which  accompany 
them. — The  form  of  the  contracted  human  heart  is  that 
of  a  cone,  of  which  the  base  is  elliptical  and  the  apex 
rounded  off;  in  the  relaxed  state  the  heart  assumes  the 
form  of  the  wedge-shaped  space  in  which  it  is  contained. 
It  approaches  the  anterior  wall  of  the  chest  in  ex- 
piration, and  recedes  in  inspiration.  In  systole  the  ven- 
tricles suddenly  draw  themselves  together  towards  a  part 
of  the  septum  which  is  about  two-thirds  of  the  way  from 
the  auriculo-ventricular  groove  to  the  apex. 

On  grasping  the  contracting  heart  of  an  animal  it  is  felt 
to  widen  and  become  harder.  The  impulse  is  due  to 
these  changes  of  form  and  consistency.  It  is  felt  most 
strongly  between  the  fifth  and  sixth  cartilages. 

Each  heart  period  is  divided  into  two  parts,  the  period 


THE    HEART.  6/ 

of  repose  and  that  of  action.  The  period  of  rest  com- 
mences with  the  closure  of  the  sigmoid  valve.  Its 
duration  varies  according  to  the  frequency  of  the  con- 
tractions. During  the  whole  of  it,  the  cavities  fill  with 
blood.  The  period  of  action,  of  which  the  duration  in 
man  is  rather  more  than  four-tenths  of  a  second,  com- 
mences with  the  auricular  systole.  About  one-tenth  of  a 
second  later,  the  ventricular  systole  begins :  thereupon 
the  auriculo-ventricular  valves  close  and  the  blood  is 
suddenly  ejected  into  the  aorta  and  pulmonary  artery. 
At  the  end  of  the  ventricular  systole,  which  lasts  about 
three  and  a  half  tenths  of  a  second,  the  ventricle  sud- 
denly relaxes. 

The  lateral  pressure  in  the  auricles  is  about  equal  to 
that  of  the  atmosphere.  It  rises,  however,  slightly  in 
auricular  systole,  attaining  its  maximum  at  the  com- 
mencement of  ventricular  systole.  In  the  ventricles  the 
pressure  sinks  below  that  of  the  atmosphere  immediately 
after  the  sigmoid  valves  close  ;  at  the  moment  of  systole 
it  rises  above  the  pressure  in  the  aorta. 

Each  action  of  the  heart  is  accompanied  by  two  sounds. 
The  first  is  produced  by  two  causes,  the  muscular  con- 
traction and  the  sudden  tightening  of  the  heart.  The 
second  sound  is  due  to  the  tightening  of  the  aorta  and 
sigmoid  valves. 

The  filling  of  the  right  ventricle  may,  in  the  normal 
state,  be  attributed  to  the  influence  of  the  elasticity  of 
the  lungs,  and  in  its  absence  to  the  pressure  in  the 
systemic  venous  system.  The  filling  of  the  left  ventricle 
is  mainly  due  to  the  pressure  in  the  pulmonary  veins, 
and  to  the  "  aspirating  power  "  of  the  ventricle  itself.  It 
is  supposed  by  Briicke  to  be  aided  by  the  distension  of 
the  coronary'  arteries. 

It  is  probable  that  about  195  grammes  of  blood  are 
discharged  by  the  left  ventricle  at  each  contraction. 
If  the  lateral  pressure  in  the  aorta  were  equal  to  that  of 

F  2 


68  RESPIRATION. 

a  column  of  blood  two  metres  in  height,  the  work  done 
by  the  left  ventricle  in  each  systole  would  amount  to  about 
four-tenths  of  a  kilogramme- meter,  without  counting  any 
work  done  within  the  heart  itself. 


Respiration. 

The  alternating  in-flow  and  out-flow  of  air,  which  con- 
stitute respiration,  result  from  the  action  of  muscles  which, 
by  changing  the  capacity  of  the  chest,  produce  corre- 
sponding, though  not  necessarily  proportional,  variations 
of  the  capacity  of  the  thoracic  air  cavity.  In  the  state  of 
rest,  that  is  when  the  chest  is  not  acted  on  by  contracting 
muscles,  its  capacity  is  determined  by  the  opposed  trac- 
tions of  elastic  structures  in  a  state  of  tension — namely, 
that  of  the  lungs,  which  tends  to  diminish  it,  and  those  of 
the  ribs  and  cartilages,  intercostal  muscles,  and  diaphragm, 
which  tend  to  enlarge  it.  The  capacity  which  the  chest 
possesses  under  this  condition  is  called  the  capacity  of 
eqinlibrmm.  In  ordinary  tranquil  breathing  the  chest  is 
expanded  beyond  its  equilibrium  capacity  in  inspiration, 
but  returns  to  it  in  expiration.  The  muscles  by  which 
this  is  effected  are  the  diaphragm  and  the  scaleni,  which 
act  by  increasing  the  vertical  diameter  of  the  chest,  and 
the  external  intercostals,  levatores,  and  intercartilaginous 
internal  intercostals,  which  increase  its  girth.  When  a 
larger  exchange  of  air  is  required  by  the  organism 
than  can  be  thus  secured,  other  inspiratory  muscles 
come  into  play,  which,  by  their  combined  action,  aid  in 
the  expansion  of  the  chest  in  inspiration,  while  in  expir- 
ation the  whole  visceral  cavity  is  constricted  by  the 
action  of  the  muscles  of  the  abdominal  wall,  of  the  lower 
internal  intercostals,  of  the  serrati  postici  inferiores,  and 
of  the  sacro-lumbales — in  consequence  of  which  action  the 
chest  acquires  in  expiration  a  capacity  less  than  that  of 
equilibrium. 


RESPIRATION.  69 

In  tranquil  breathing  the  glottis  is  motionless,  but  in 
the  more  active  modes  of  respiration,  the  cords  diverge  in 
inspiration,  resuming  their  normal  position  in  expiration. 
In  extreme.dyspnoea,  inspiration  is  accompanied  by  dila- 
tation of  the  nostrils. 

The  lungs,  mechanically  considered,  may  be  regarded  as 
a  collection  of  elastic  and  very  distensible  bags,  all  of  which 
communicate  freely  with  each  other  as  well  as  with  the 
atmosphere.  The  volume  of  each  lung,  when  removed 
from  the  chest,  is  much  smaller  than  that  of  the  cavity  in 
which  it  is  contained,  and  which,  in  its  normal  state  of 
expansion,  it  completely  fills  ;  consequently,  when  a  pleural 
cavity  is  opened,  the  lung  collapses.  When  the  closed 
pleura  is  brought  into  communication  with  a  mercurial 
manometer,  the  column  in  the  open  limb  falls,  so  that  the 
pressure  to  which  any  fluid  in  this  cavity  is  exposed  is  less 
than  that  of  the  atmosphere.  As  measured  when  the 
chest  is  in  the  condition  of  equilibrium,  the  difiference  can 
be  shown  to  be  about  i-^-q  of  an  atmosphere  (7  millimeters 
mercury).  In  natural  inspiration  it  increases  to  8  or  9 
millimeters,  and  in  full  inspiration  it  may  be  increased  to 
30  millimeters.  It  is  increased  by  any  cause  which  de- 
stroys the  expansibility  of  any  part  of  the  lung. 

As  the  organs  contained  in  the  chest  are  under  the  same 
pressure  as  the  fluid  in  the  pleura,  the  flow  of  blood  towards 
the  heart  is  aided  by  the  elasticity  of  the  lungs.  The  same 
condition  is  also  favourable  to  the  diastolic  filling  of  the 
heart,  which  contracts  with  more  effect  after  each  inspira- 
tion, so  that  the  arterial  pressure  rises. 

An  adult  male  inspires  from  25  to  30  cubic  inches  at 
a  time,  and  about  20  times  per  minute  ;  consequently, 
from  500  to  600  cubic  inches  per  minute.  The  greatest 
volume  of  air  which  an  individual  is  able  to  exchange 
in  a  breath  is  called  the  "vital  capacity."  The  mean 
"vital  capacity"  of  a  man  of  ordinary  height  and  build 
(5    feet    7    inches,  and    32    inches    in    girth)    is  210  cubic 


70  BODILY   MOTION. 

inches  =  3480  cubic  centimeters.  A  woman  5  feet  5  inches 
in  height  and  of  average  girth,  has  a  vital  capacity  of 
not  more  than  160  cubic  inches.  From  observations 
made  on  a  large  number  of  male  adults  of  ordinary- 
heights,  it  has  been  found  that  on  the  whole  the  vital 
capacity  varies  according  to  the  height  of  the  individual, 
in  such  a  way  that  a  difference  of  i  inch  in  height 
makes  a  difference  of  150  centimeters,  i.e.  about  9 
cubic  inches  in  vital  capacity ;  and  further,  that  be- 
tween two  men  of  the  same  height,  but  different  girth, 
there  will  be  a  difference  of  about  the  same  amount, 
viz.,  9  cubic  inches  for  every  inch  difference  in  girth. 
Similar  laws  have  been  found  to  hold  good  as  regards 
female  adults.  In  individual  instances  this  result  is 
much  affected  by  the  flexibility  of  the  chest,  the  mus- 
cularity of  the  individual,  and  other  circumstances,  the 
influence  of  which  it  is  difficult  to  estimate.  After  the 
most  complete  expiration  possible,  a  quantity  of  air  re- 
mains in  the  thorax,  which  is  sometimes  called  "  residual," 
and  amounts  to  about  90  cubic  inches.  In  the  equilibrium 
position  the  chest  contains  about  190  cubic  inches ;  when 
fully  expanded,  about  300,  of  which  210  can  be  expelled. 

Two  sounds  are  heard  in  listening  to  the  normal  chest, 
viz.,  the  vesicular  inspiration  sound,  and  the  bronchial 
sound,  which  is  chiefly  expiratory.  The  former  has  its 
seat  in  the  infimdibnla,  the  latter  in  the  riina  glottidis.  In 
each  case  the  production  of  the  sound  is  dependent  on  the 
sudden  widening  of  the  channel  along  which  the  air  flows. 


Bodily  Motion. 

Action  of  Voluntary  Muscles  o?t  the  Skeleton. — With  the 
exception  of  those  cases  in  which  voluntary  muscles  act 
peristaltically,  the  effect  of  muscular  contraction  in  produc- 
ing motions  of  the  whole  body,  or  of  parts  of  it,  is  always 


BODILY   MOTION.  7 1 

dependent  on  approximation  of  the  ends  of  the  muscles 
concerned.  The  direction  and  extent  of  these  motions  are 
regulated  by  the  forms  of  the  movable  bones,  and  of  the 
symphyses  or  of  the  joints  by  which  they  are  connected 
with  the  rest  of  the  skeleton.  The  term  symphysis  is  appli- 
cable to  the  connection  of  two  bones  by  a  perfectly  elastic 
material,  in  such  a  way  that,  after  having  been  bent  or 
twisted  on  each  other,  they  tend  to  recover  their  relative 
normal  position.  The  only  example  of  this  in  the  human 
skeleton  is  that  of  the  bodies  of  the  vertebrae.  The  essen- 
tial difference  between  the  joint  and  the  symphysis  consists 
in  this — that  in  the  former  the  bones  have  no  normal 
relation  to  each  other,  but  assume  with  equal  readiness 
any  among  the  infinite  number  of  relative  positions  which 
the  structure  of  the  joint  allows. 

Joints  are  divisible  into  those  which  have  a  single  axis 
of  rotation  (hinge  joints)  and  those  which  have  several 
axes  (ball-and-socket  joints).  It  is  essential  to  the  efficient 
working  of  a  joint  of  either  kind  (i)  that  the  two  surfaces 
should  be  kept  in  apposition  ;  and  (2)  that  the  movements 
of  the  bones  on  each  other  should  be  restrained  within 
due  limits  ;  accordingly  contrivances  exist  in  all  joints  for 
these  two  purposes. 

The  efficiency  of  the  action  of  a  muscle  in  producing 
motion  about  a  joint  depends  on  the  mode  of  its  attach- 
ment to  the  bones.  In  all  cases  the  effect  produced  is  to 
the  force  exerted,  as  the  distance  of  the  nearest  point 
of  the  straight  line  ivJiicJi  co?inects  the  origin  with  the 
insertion  of  the  contracting  muscle  from  the  axis  of 
rotation  of  the  joint  is  to  the  distance  from  the  joint  to  the 
insertion  of  the  muscle. 

The  maintenance  of  the  erect  posture  is  dependent  on 
constant  muscular  exertion,  for  the  line  of  gravity  of  the 
head  falls  far  in  front  of  the  condyles  of  the  occipital  bone, 
that  of  the  head  and  trunk  together  behind  the  line  which 
joins  the  hip  joints,  that  of  the  whole  body,  in  front  of  the 


72  VOICE   AND   SPEECH. 

ankle  joint.  As  regards  each  of  these  parts,  excepting  the 
head,  the  supporting  muscles  are  aided  by  the  forms  of  the 
joints  and  the  arrangement  of  the  ligaments.  In  sitting, 
the  body  if  unsupported  in  front  or  behind  is  balanced  on 
the  tubera  iscJiii. 

In  walking,  the  position  of  the  advancing  or  acting  limb 
at  the  beginning  of  each  step,  is  represented  by  the  vertical 
side,  the  following  limb  by  the  hypothenuse  of  a  right- 
angled  triangle,  of  which  the  base  is  a  step  or  pace,  and 
the  apex  is  in  the  position  of  the  hip-joint :  at  the  same 
moment  the  knee  and  ankle  joints  are  flexed.  Towards 
the  end  of  each  step,  both  joints  become  strongly  extended. 
During  each  step  the  pressure  of  the  foot  upon  the  ground 
increases  towards  the  end  :  the  pelvis  oscillates  once  from 
side  to  side  and  twice  up  and  down,  for  every  two  paces,  i.e. 
in  each  period  of  progression.  In  walking  there  is  no 
interval  during  which  the  weight  of  the  body  is  unsup- 
ported :  in  running  an  interval  exists,  the  relative  length 
of  which  increases  as  the  pace  quickens. 


Voice  and  Speech. 

The  movements  of  the  thyroid  and  arytenoid  cartilages 
by  which  the  form  of  the  glottis  and  the  tension  of  the 
cords  are  modified,  are,  (i)  rotation  of  the  thyroid  on  its 
horizontal  axis  ;  (2)  rotation  of  each  arytenoid  on  its 
vertical  axis  ;  and  (3)  rotation  of  each  arytenoid  on  its 
horizontal  axis.  The  first  produces  tightening  or  relax- 
ation of  the  cords,  the  second,  opening  or  closure  of  the 
vocal  glottis.  By  the  third,  the  arytenoid  cartilages  are 
approximated  to  or  withdrawn  from  each  other  so  as 
to  vary  the  width  of  the  space  between  them. 

It  is  the  principal  function  of  the  glottis  to  produce 
those  "  compound  musical  tones  "  to  which  in  physiology 
we  apply  the  term  "  voice."     These,  when  modified  by  the 


VOICE   AND   SPEECH.  Tl 

mouth  SO  as  to  become  articulate,  constitute  "speech." 
Articulation  consists  in  the  production  of  certain  sounds 
in  the  mouth  and  pharynx  which  arc  either  associated 
with  voice  (as  in  speaking  aloud),  or  constitute  all  that  is 
heard  (as  in  whispering).  These  sounds  are  distinguished 
as  vowels  and  consonants.  Vowel  sounds  dififer  from  con- 
sonant sounds  in  possessing  the  characters  of  musical 
tones,  and  may  accordingly  be  distinguished  by  the  rela- 
tive vibration  rates  of  the  tones  which  constitute  them. 
Each  vowel  has  its  own  pitch  or  tone.  To  produce  any 
vowel  sound,  such  form  must  be  given  to  the  cavity  of  the 
mouth  and  pharynx  as  to  render  it  a  "  resonator"  for  the 
tone  which  is  characteristic  of  the  vowel  to  be  produced. 
Consonants  are  modifications  of  the  voice  or  whisper  caused 
by  the  passage  of  air  through  constricted  or  valvular  parts 
of  the  mouth  or  fauces.  They  derive  their  characters 
from  the  duration  and  order  of  succession  of  the  sounds 
which  constitute  them.  They  are  produced  by  the  soft 
palate,  tongue  or  lips.  They  are  divisible  into  four  groups, 
viz.  (i)  valve  sounds,  (2)  blowing  sounds,  (3)  nasal  sounds, 
(4)  vibrating  sounds.  Of  these  groups  each  of  the  sounds 
belonging  to  the  first  and  second,  presents  itself  in  a  soft 
and  a  hard  modification,  of  which  the  former  cannot  be 
adequately  produced  in  a  whisper.  This  classification 
does  not  include  the  aspirate  H,  which  consists  in  the 
production  of  an  expiratory  sound  in  the  larynx,  imme- 
diately preceding  that  of  the  vowel  sound  aspirated. 


Part  III. 
FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Nerves. 

The  organs  of  the  nervous  system  of  which  the  functions 
are  known  are  (i)  Reflex  centres  ;  (2)  End-organs  ;  and 
(3)  Conducting  organs.  The  most  important  conducting 
organs  are  nerves.  A  nerve  is  made  up  of  fibres,  each  of 
which  consists  of  axis  cyhnder,  medullary  sheath  and  nu- 
cleated sheath.  The  medullary  sheath  is  divided  into 
lengths  by  septa  at  equal  intervals,  but  the  axis  cylinder 
is  continuous.  The  axis  cylinder  consists  chiefly  of  pro- 
teid,  the  medullary  sheath  of  material  for  the  most  part 
soluble  in  ether. 

Living  nerve  exhibits  in  itself  three  properties  which 
appear  to  be  characteristic — (i)  that  when  injured  so  as 
to  produce  solution  of  continuity  of  its  fibres,  the  injured 
part  is  electrically  negative  to  the  uninjured,  (2)  that 
when  a  nerve  is  excited,  this  electrical  property  is  modified, 
the  modification  thus  produced  characterising  the  state  of 
excitation,  and  (3)  that  this  state  can  be  propagated  along 
the  fibre  in  both  directions.  With  reference  to  the  state 
of  excitation,  two  inferences  are  allowable,  viz.,  (i)  that  the 
electrical  change  exists  in  uninjured  nerves,  although  it  is 
imperceptible,  and  (2)  that  it  is  associated  with  a  chemical 
change. 

The  state  of  excitation  is  capable  of  being  propagated 
from  the  nerve  originally  excited  to  excitable  end-organs^ 
namely,  in  the  case  of  efferent  nerves,  to  muscle  or  gland, 
and  in  the  case  of  afferent  nerves  to  centres.     In  this  way 


NERVES.  75 

it  manifests  itself  outside  of  the  nerve,  either  in  the  produc- 
tion of  motions,  secretions,  reflexes,  or  states  of  conscious- 
ness. The  excitability  of  a  nerve  admits  of  being 
measured  by.,  ascertaining  the  minimum  excitation  by 
which  the  signs  of  the  excitatory  state  can  be  evoked. 
For  this  purpose  the  exciting  agent  used  must  be  measur- 
able. In  the  case  of  nerves  of  voluntary  muscles,  the 
excitability  can  also  be  judged  of  by  measuring  the  degree 
of  shortening  of  the  muscle  produced. 

When  the  circulation  ceases  in  a  nerve  or  in  the  whole 
body,  its  vital  properties  alter.  Its  excitability  at  first 
increases,  then  gradually  declines,  until  it  is  extingui.shed. 
These  changes  take  place  in  the  same  order  in  all  nerves, 
but  occur  earlier  in  parts  nearest  the  centres  (Ritter  and 
Valli)  ;  thus  the  intra-muscular  parts  of  motor  nerves 
survive  longest.  Injury  of  a  nerve  produces  increase  of 
excitability  in  the  neighbourhood.  The  extinction  of 
excitability  of  a  living  nerve  consequent  on  cessation  of 
circulation,  is  immediately  followed  by  structural  changes 
affecting  chiefly  its  medullary  sheath. 

In  a  similar  manner  loss  of  excitability  and  consequent 
change  of  structure,  are  produced  by  severance  of  a  nerve 
from  the  cerebro-spinal  centres.  It  is  believed  that  they 
may  also  result  from  want  of  exercise.  Nerve  is  more 
excitable  and  more  vulnerable  than  muscle,  but  is  less 
affected  by  want  of  blood  supply  and  less  readily 
exhausted  by  repeated  excitation.  The  two  last  facts 
indicate  that  its  exchange  of  material  is  much  less 
active. 

Influence  of  the  voltaie  current  on  excitability. — (i.)  Under 
the  influence  of  a  constant  current  flowing  along  a  nerve, 
its  excitability  is  increased  near  the  negative  pole  (cathode), 
decreased  near  the  positive  pole  (anode),  but  the  nerve  is, 
as  a  rule,  not  excited  so  long  as  the  intensity  does  not  vary. 
(2.)  Every  variation  of  intensity  of  a  current  so  directed 
excites  the  nerve.     Other  things  being  equal,  the  degree 


76  NERVES. 

of  effect  produced  is  the  greater,  the  shorter  the  time  occu- 
pied in  the  variation.  No  effect  is  produced  if  the  current 
is  transverse.  (3.)  If  the  current  is  of  moderate  intensity, 
the  excitation  occurs  at  make  and  break  whatever  its 
direction — the  make  excitation  starting  from  the  cathode, 
the  break  from  the  anode.  (4.)  If  the  current  is  strong, 
the  make  excitation  is  suppressed  when  the  current  is  from 
the  muscle  ;  the  break  excitation  when  it  is  towards  the 
muscle.  (5.)  If  the  current  is  weak,  there  is  no  excitation 
excepting  at  make.  The  propositions  3,  4,  and  5  constitute 
the  so-called  "  Law  of  contraction."  (Pfliiger.)  If  the 
current  lasts  long  and  is  of  great  intensity,  reversed  after 
effects  manifest  themselves  on  its  cessation.  Thus  there  is 
increased  excitability  at  the  anode  which  may  lead  to 
excitation  and  manifest  itself  in  contraction  (Ritter's 
Tetanus).  This  contraction  is  increased  by  reclosing  the 
current  in  the  opposite  direction — annulled  by  reclosing  it 
in  the  same  direction. 

The  above  experimental  facts  constitute  the  basis  of  the  doctrine  of  Elec- 
trotonus.  The  contrast  between  the  two  opposite  states  (called  Cathelec- 
trotonus  and  Anelectrotonus)  referred  to  in  (i),  is  most  easily  observed  in  the 
parts  of  the  nerve  which  are  immediately  beyo7id  the  limits  of  the  part  through 
which  the  current  passes ;  but  it  can  also  be  studied  in  the  intrapolar  part. 
Here  it  is  found  that  the  cathelectrotonic  effect  diminishes  in  extent,  and  that 
the  anelectrotonic  increases  as  the  current  becomes  stronger.  The  statement 
(4)  is  satisfactorily  explained  on  the  ground  that  the  propagation  of  the  make 
excitation  which  originates  at  the  cathode,  is  hindered  by  the  anelectrotonus 
which  exists  at  the  anode,  and  that  in  like  manner  the  break  excitation  is 
interrupted  in  consequence  of  the  after  effect  at  the  cathode.  The  fact  re- 
corded in  (5)  which  occurs  invariably,  simply  means  that  the  cathodic  excita- 
tion is  stronger  than  the  anodic. 

Methods  and  Processes  of  Excitation. — (i)  A  motor 
nerve  may  be  excited  by  the  closing  or  opening  of  a  vol- 
taic current  flowing  along  it ;  (2)  by  any  change  in  the 
intensity  of  such  a  current  ;  (3)  by  the  passage  along  it  of 
an  induction  current ;  (4)  by  the  passage  of  a  succession 
of  induction  currents  in  alternately  opposite  directions 
(Faradization) ;  (5)  mechanically — either  by  a  single  per- 


NERVES.  ^^ 

cussion  or  by  a  rapid  succession  of  percussions  (Heiden- 
hain)  ;  (6)  by  chemical  agents  which  cither  deprive  the 
nerve  of  water  or  disintegrate  it. 

In  all  measurable  modes  of  excitation,  the  muscular 
effect  increase's  with  the  stimulus  up  to  a  certain  limit, 
beyond  which  there  is  no  further  augment.  Excitations 
just  sufficient  to  produce  the  maximum  effect  arc  called 
"maximal";  others  "over  maximal"  or  "minimal"  as 
the  case  may  be.  The  effect  of  a  minimal  excitation  is 
increased  when  the  seat  of  excitation  is  in  catJiclectrotonos  ; 
the  effect  of  a  maximal  is  diminished  when  it  is  in  aticlcc- 
trotonos. 

Excitation  of  one  or  more  of  the  constituent  fibres  of  a 
nerve  is  without  effect  on  the  others  :  it  is  incapable  of 
propagation  from  the  excited  fibre  to  any  other  struc- 
ture excepting  the  end-organ  in  which  it  terminates. 

The  phenomena  known  as  the  "  paradoxical  twitch  "  and  the  "  secondary 
twitch  from  the  nerve,"  which  are  apparent  exceptions  to  the  above  statement, 
are  due  to  electrotonic  variation. 

If  by  the  myograph  or  otherwise  the  time  is  measured 
which  elapses  between  an  instantaneous  excitation  of  a 
motor  nerve  and  the  beginning  of  the  contraction  of  the 
muscle  which  it  supplies,  first  with  the  seat  of  excitation 
close  to  the  muscle,  and  then  with  the  seat  of  excitation 
at  2 '6  centims.  distant,  it  is  found  that  there  is  a  slight 
difference  amounting  to  about  one-thousandth  of  a  second 
between  the  two  measurements. 

Living  nerve  is  electromotive.  The  phenomena  closely 
agree  Avith  those  of  muscle.  In  an  undivided  nerve  no 
electrical  differences  manifest  themselves  either  in  the 
normal  state  or  during  excitation.  In  a  severed  nerve, 
the  cut  surface  is  found  to  be  negative  to  the  sound  sur- 
face ;  the  difference  is,  however,  much  less  than  in  muscle. 
An  instantaneous  excitation  of  any  part  of  a  severed 
ner\'e  produces  a  momentary  diminution  of  the  relative 


y8  NERVE-CENTRES. 

negativity  of  the  cut  surfaces  (negative  variation).  The 
time  at  which  this  happens  depends  on  the  distance 
between  the  seat  of  excitation  and  the  section.  The  rate 
of  propagation  of  the  negative  variation  as  measured  by 
the  "rheotome"  (Bernstein),  agrees  with  that  of  the  trans- 
mission of  the  excitatory  state  in  a  motor  nerve,  as 
measured  by  the  myograph. 

Electrotonic  vmdation  of  the  nerve  current, — If  during 
the  passage  of  the  voltaic  current  through  the  central  part 
of  a  length  of  nerve,  the  extra-polar  parts  are  investigated, 
electrical  differences  show  themselves  which  have  the  same 
direction  as  those  which  are  produced  by  the  current  in 
the  inter-polar  tract. 


Functions  of  Nerve-Centres. 

By  the  term  "centre"  are  designated  certain  parts  of 
the  Brain  or  Spinal  Cord,  respecting  each  of  which  it  is 
known  that  it  is  concerned  in  the  regulation  or  control  of 
some  one  of  the  chemical  or  mechanical  processes  of  the 
living  organism.  Our  knowledge  of  the  limits  and  topo- 
graphical relations  of  these  parts,  and  of  the  channels 
by  which  they  mutually  influence  each  other,  and  the 
organs  over  which  they  preside,  is  derived  almost  exclu- 
sively from  experiments  on  living  animals. 

Nerve  centres  are  excitable  organs  which  owe  their 
physiological  endowments  to  the  nerve  cells  and  reticulum 
of  which  they  consist,  and  to  the  connection  of  these 
structures  with  afferent  and  efferent  nerves.  The  excita- 
tory state  originates  in  them  for  the  most  part  by  pro- 
pagation from  afferent  nerves,  or  from  other  centres,  and 
is  propagated  by  them  to  other  centres  or  to  efferent 
nerves. 

This  process  is  designated  "  reflex  action  ;"  a  term  which 
is  applied  to   any  case  in  which  the  function  of  a  mus- 


NERVE-ChNTRES.  79 

cular,  glandular,  or  other  organ  is  called  into  activity  or 
arrested  in  consequence  of  the  excitation  of  an  afferent 
nerve. 

The  most  important  reflex  actions  are  muscular.  These 
are  of  two  kinds,  which  may  be  called  normal  and 
abnormal.  Normal  reflex  processes  spring  from  the 
excitation  of  one  or  more  peripheral  sense-organs,  by 
usually  feeble  stimuli.  They  are  characterized  by  the  fact 
that  excitations  of  the  same  kind,  originating  from  the 
same  end-organs  always  lead  to  the  same  results,  that  is, 
occasion  the  same  coDibinations  or  series  of  co-ordinated 
muscular  actions.  This  fact  justifies  the  hypothesis  that 
in  the  centres  there  are  channels  of  propagation,  by  which 
the  excitatory  process  is  guided,  notwithstanding  that 
our  present  knowledge  of  anatomy  affords  no  clues  by 
which  they  may  be  traced.  All  normal  reflex  processes 
are  adapted  to  the  accomplishment  of  useful  purposes  in 
the  animal  economy. 

Abnormal,  incoordinate,  or  convulsive  reflex  processes, 
do  not  occur  in  the  healthy  body,  excepting  in  consequence 
of  injury.  The  excitatory  state  which  here  as  in  the  other 
case  is  communicated  to  the  centre  by  an  afferent  nerve, 
spreads  from  it  to  other  centres  by  mere  continuity  of 
structure,  irrespectively  of  channels  of  propagation.  Con- 
sequently those  centres  which  are  nearest,  are  as  a  rule 
first  affected,  and  in  their  turn  the  motor  nerves  which 
spring  from  them  and  the  muscles  to  which  such  nerves  are 
distributed,  without  distinction  of  function.  In  the  abnormal 
state,  whether  induced  by  loss  of  blood,  by  interference 
with  respiration,  by  disease,  or  by  poisons,  incoordinate 
reflexes  may  be  excited  by  the  action  of  ordinary  stimuli 
on  sensory  end-organs,  but  much  more  readily  by  injuries 
of  nerve  trunks. 

The  time  occupied  by  normal  reflexes  varies  according 
to  their  complexity,  and  to  the  remoteness  of  the  centres 
concerned,  from  a  twentieth  to  a  tenth  of  a  second,  or  even 


80  SPINAL   NERVE-ROOTS. 

more.     Of  this  time,  all  but  about  a  hundredth  of  a  second 
is  occupied  in  the  central  process. 

It  is  often  observed  that  the  muscular  effect  produced 
by  the  excitation  of  one  afferent  nerve  is  hindered  or 
delayed  by  excitation  of  another.  This  phenomenon  is 
called  inhibition.  This  may  be  attributed  either  to  the 
counteraction  of  two  centres,  or  to  the  counteraction  of 
two  excitations  in  the  same  centre. 

Our  knowledge  of  both  kinds  of  reflex  action  is  largely  derived  from  the 
observation  of  the  phenomena  exhibited  by  the  body  of  the  frog  after  the 
animal  has  been  killed  by  removing  the  brain.  In  preparations  of  this  kind 
it  is  seen  (i)  that  definite  series  or  groups  of  muscular  actions  adapted  to 
purposes,  occur  in  response  to  excitation  of  particular  spots  of  the  cutaneous 
surface  ;  (2)  that  slight  excitations  so  applied,  act  by  summation,  i.e.,  do  not 
produce  any  effect  until  they  have  lasted  for  some  time  ;  (3)  that  the  excitation 
of  the  central  ends  of  nerve  trunks  produces  irregular  or  convulsive  reflexes, 
the  extent  of  which  varies  according  to  the  intensity  of  the  excitation  ;  (4) 
that  under  the  influence  of  strychnine,  similar  effects  are  produced,  by  ordinary 
cutaneous  stimuli ;  (5)  that  by  acting  directly  on  the  "convulsive  centre"  in 
the  medulla  oblongata,  or  by  faradization  of  the  whole  cord,  general  con- 
vulsion is  produced,  similar  to  the  partial  effects  above  described  {see 
Practical  Exercises). 

Functions  of  the  Roots  of  the  spinal  nerves  and  of  their 

Ganglia. 

It  was  discovered  by  Charles  Bell,  in  18 11,  that  mechanical 
irritation  of  the  anterior  roots  of  the  spinal  nerves,  pro- 
duced convulsive  movements  of  the  muscles  to  which  they 
were  distributed.  More  than  ten  years  later,  Magendie 
discovered  that  excitation  of  the  posterior  roots  produced 
pain,  and  occasioned  reflex  contractions  of  the  muscles, 
and  that  these  were  prevented  by  section  of  the  anterior 
roots  :  subsequently  he  discovered  that  in  mammals  after 
severance  of  an  anterior  root,  excitation  of  the  peripheral 
end  influences  the  cord  through  the  trunk  and  posterior 
root  of  the  same  nerve.  In  the  frog  the  anterior  roots 
are  exclusively  afferent. 

Of  the   function  of  the  gan  glia  of  the  posterior  roots 


THE  SPINAL  CORD.  8 1 

nothing  is  known,  excepting  that  severance  of  a  ganglion 
from  the  nerve  trunks  to  which  it  belongs,  produces  loss  of 
excitability  and  structural  changes  in  afferent  fibres  of  the 
nerve.  (Waller.) 


Functions  of  the  ivhite  columns  of  the  Spinal  Cord. 

The  most  important  anatomical  facts  relating  to  the  channels  by  which 
excitation  is  transmitted  in  the  spinal  cord,  are  (i)  that  the  fibres  of  the 
spinal  nerves  are  not  continued  to  the  brain,  but  communicate  with  ganglionic 
cells  ;  (2)  that  in  the  anterior  roots  this  communication  is  direct,  mediate  in 
the  posterior,  i.e.  through  the  reticulum  ;  (3)  that  the  anterior  roots  may  be 
traced  through  the  anterior  horns,  to  the  anterior  columns  of  the  other  side 
by  the  white  commissure,  as  well  as  to  the  anterior  and  lateral  columns  of  the 
same  side  ;  {4)  that  the  fibres  of  the  posterior  roots  divide  into  two  sets,  of 
^vhich  the  smaller  at  once  lose  themselves  in  the  substantia  gelatinosa,  the 
larger  division  tending  inwards  towards  the  posterior  columns,  in  which  some 
of  the  fibres  appear  to  acquire  a  vertical  direction  ;  (5)  the  sectional  area  of 
the  lateral  columns  of  the  spinal  cord  is,  as  measured  at  any  part  of  its  course, 
proportional  to  the  sum  of  the  sectional  areas  of  the  nerves  which  enter  it 
below  the  section  ;  (6)  the  sectional  area  of  the  grey  substance  is  proportional 
to  the  sum  of  the  sectional  areas  of  the  nerves  which  enter  the  cord  in  the 
neighbourhood  of  the  section. 

The  most  important  results  of  experimental  investigation 
as  to  the  channels  of  propagation  in  the  cord  may  be  stated 
as  follows  : — (i.)  The  fibres  of  the  lateral  columns  are  the 
only  channels  of  influence  between  the  intra-cranial  centres 
and  the  lower  limbs.  (2.)  The  afferent  fibres  by  which 
excitation  of  either  lower  extremity  influences  the  intra- 
cranial centres,  are  contained  in  the  lateral  columns  of  the 
opposite  side.  (3.)  The  fibres  by  which  the  intra-cranial 
centres  influence  the  muscles  of  either  inferior  extremity 
are  contained  for  the  most  part  in  the  lateral  column  of 
the  same  side.  (4.)  It  is  probable  that  the  fibres  of  the 
anterior  and  posterior  columns  serve  as  channels  of  com- 
munication between  neighbouring  parts  of  the  cord. 
There  is  reason,  however,  for  believing  that  in  the  lumbar 
region,  the  posterior  columns  contain  fibres  by  which 
sensory  impressions  arc  transmitted  upwards. 

G 


82  RESPIRATORY   CENTRE. 

The  spinal  cord  is  entirely  insensible  to  mechanical 
stimulation  excepting  in  the  immediate  neighbourhood  of 
its  motor  roots.  Its  grey  substance  seems  to  be  also 
wholly  insusceptible  of  electrical  stimulation,  but  its  fibres 
can  be  excited  either  by  single  induction  shocks  or  by 
faradization. 


Centres  of  the  Medulla  Oblongata. 

The  central  canal  of  the  cord  opens  out  into  the  rhomboidal  space,  or 
fourth  ventricle,  the  two  grey  columns  (horns)  thus  becoming  superficial,  and 
assuming  such  a  position  that  what  was  before  posterior  lies  outside.  In  the 
stratum  of  grey  substance  thus  exposed,  are  contained  the  regulatory  centres 
which  preside  over  the  most  important  functions  of  the  body,  namely  those  of 
the  heart,  of  the  arteries,  of  the  respiratory  organs,  of  the  organs  of  digestion, 
of  speech,  of  taste,  and  of  locomotion.  The  origins  of  the  nerves  concerned 
in  the  functions  of  these  centres  are  in  close  relation  with  each  other,  but 
nothing  precise  is  known  of  their  anatomical  relations. 

The  regulatory  centre  for  the  heart  is  represented  by  two  tracts  of  grey 
substance  on  either  side  of  the  spinal  canal,  but  nearer  to  the  posterior  sur- 
face. At  the  cal.  sa-ipt.  these  diverge  and  become  continuous  with  the  vagal 
tracts  (al(E  cinerecz)  which  are  separated  from  each  other  by  the  nuclei  of  the 
hypoglossal  nerve.  Each  vagal  tract  is  in  relation  at  its  upper  end  with  the 
nucleus  of  the  glossophaiyngeal  nerve,  which  is  close  to  the  auditory  striae. 
Outside  of  each  vagal  tract  are  the  internal  and  external  nuclei  of  the  auditoiy 
nei-ve,  which  are  respectively  continued  downwards  into  the  grey  tubercle  of 
Rolando  and  the  restifomi  nucleus.  Higher  up,  the  internal  auditory  nucleus 
becomes  continuous  with  the  origin  of  the  sensoiy  division  of  the  trigeminus, 
the  motor  division  of  which  springs  from  the  grey  substance  nearer  the  middle 
line.  The  hypoglossal  nucleus  is  continuous  with  those  of  the  abducens  and 
facial,  which  lie  underneath  the  eminentia  teres  of  each  side,  and  is  in  relation 
externally  with  the  origin  of  the  motor  root  of  the  trigeminus.  The  same 
motor  tract  is  continuous  upwards  with  the  grey  substance  underneath  the 
floor  of  the  aqueduct,  from  which  the  oculomotorius  and  trochlearis  spring. 

Influence  of  the  Nervous  System  on  respiration. — The 
respiratory  nervous  system  consists  of  {a)  the  regulatory 
centre  (vagal  tracts)  ;  ib)  the  afferent  fibres  of  the  vagus ; 
{c)  motor  fibres  contained  in  the  facial  and  recurrent,  as 
well  as  in  the  phrenic,  intercostal,  and  other  spinal  nerves, 
(i.)  Destruction  of  the  vagal  tracts  produces  instant  death 
in  mammalia ;  destruction  of  the  upper  part  only,  arrests 


RESPIRATORY   CENTRE.  8$ 

those  respiratory  movements  which  are  dependent  on  the 
facial  nerve :  destruction  of  the  lower  part  only,  arrests 
the  thoracic  movements.  (2,)  The  respiratory  centre  acts 
automatically,  i.e.,  is  self-acting,  but  (3)  its  activity  is  affected 
by  the  condition  of  the  circulating  blood,  in  such  a  way 
that  the  more  abundantly  it  is  supplied  with  arterial  blood 
the  less  active  are  the  respiratory  movements,  and  the  fewer 
muscles  take  part  in  them.  Accordingly  saturation  of  the 
haemoglobin  of  the  blood  with  oxygen  produces  apncea, 
i.e.,  suspension  of  respiratory  effort,  while  defective  arte- 
rialization  produces  increased  activity  of  both  centres,  i.e., 
hyperpnoea,  which,  if  prolonged  and  excessive  (dyspnoea) 
results  in  exhaustion.  (See  Asphyxia,  p.  90.)  (4.)  The 
centre  receives  through  the  vagus  trunk  two  sets  of  nerve 
fibres  which  act  upon  it  antagonistically  to  each  other.  Of 
these,  one  set  are  chiefly  contained  in  the  superior  laryngeal, 
the  other  probably  exclusively  in  nerves  distributed  to  the 
bronchial  tubes  and  lungs,  of  which  some  of  the  fibres  are 
also  inhibitory.  The  influence  of  these  fibres  may  be  under- 
stood by  supposing  either  that  the  respiratory  centre  consists 
of  two  parts,  of  which  one  is  inspiratory,  the  other  expiratory, 
and  that  the  second  of  these  acts  antagonistically  to  the 
first,  i.e.  exercises  an  inhibitory  influence  over  it,  or  that 
there  is  one  centre  of  which  the  action  is  affected  in  oppo- 
site ways,  according  as  one  or  the  other  set  of  fibres  is  ex- 
cited. (5.)  The  condition  which  produces  hyperpncea  is 
not  excess  of  COg  but  defect  of  oxygen.  (6.)  The  influence 
of  increase  of  the  temperature  of  the  blood  on  the  respi- 
ratory movements  resembles  that  of  defect  of  oxygen. 

Experimental  Proofs.—  i.  Destruction  of  the  vagal  tracts  produces  sudden 
cessation  of  respiratory  movements,  without  convulsion  ;  but  severance  of  the 
fascic.  teretes  above  the  striae  stops  only  the  respiratory  movements  of  the 
face,  the  lar}'ngeal  and  thoracic  movements  continuing.  2.  After  section  of 
both  vagi  and  of  the  cord  above  the  third  cervical  vertebra,  the  animal  dies  of 
asphyxia,  but  the  respiratory  movements  of  the  facial  muscles  and  those  of 
the  stemomastoids  continue.  3.  Section  of  both  vagi  below  the  sup.  laryng. 
produces  diminished  frequency,  increased  amplitude  and  altered  rhythm  of 
thoracic  respiratory  movements,  with   prolongation  of  each  inspiratory  act. 

G    2 


84  NERVOUS   SYSTEM, 

4.  In  artificial  respiration  the  rhythmical  action  of  the  laryngeal  and  facial 
muscles  continues,  and  follows  the  rhythm  of  the  artificial  respirations,  each 
injection  of  air  being  followed  by  expiratory  movements  of  the  nares  and 
glottis.  5.  Excitation  of  the  central  end  of  the  divided  sup.  laryng.  nerve 
always  produces  transitoiy  cessation  of  respiratoiy  movements  with  relaxed 
diaphragm.  The  same  effect  is  produced  by  injection  of  air  impregnated 
with  NH3  gas  into  the  larynx  from  below.  6.  Excitation  of  the  central  end 
of  the  divided  vagus  produces  sometimes  continuous  or  interrupted  contraction 
of  the  diaphragm,  sometimes  the  effects  described  in  5.  7.  Respiration  of  an 
atmosphere  containing  excess  of  COj  (2o7o  or  more)  does  not  produce 
dyspnoea  if  as  much  as  2o7o  of  O  be  present.  8.  Dyspnoea  is  produced  by 
warming  the  blood  w'hich  is  supplied  to  the  medulla  oblongata,  whether  the 
general  temperature  of  the  body  be  raised  or  not. 

Reflex  respiratory  movements. — Co-ordinated  respiratory 
movements  adapted  for  the  exclusion  or  expulsion  of 
irritating  substances  from  the  respiratory  cavities,  are 
determined  either  by  mechanical  or  chemical  excitation 
of  the  nares  (sneeze),  of  the  mucous  membrane  below 
and  on  either  side  of  the  epiglottis  (closure  of  the  glottis), 
or  of  the  vocal  cords  (cough),  or  of  the  bronchial  mucous 
membrane  (paroxysm  of  cough  by  summation).  In 
coughing  and  sneezing,  each  reflex  effect  consists  of  three 
acts,  viz.,  a  short  inspiration,  followed  by  a  violent  expul- 
sive burst  of  air  through  a  previously  closed  air-way,  in 
the  production  of  which  all  the  expiratory  muscles,  both 
the  constrictors  of  the  abdominal  cavity,  and  the  depres- 
sors of  the  lower  ribs,  take  part.  The  closure,  which  is 
the  second  phase  in  the  process,  takes  place  in  cough  at 
the  glottis,  in  the  sneeze  at  the  fauces.  The  afferent 
channels  concerned  in  these  reflexes  are  contained  in  the 
middle  division  of  the  trigeminus  and  the  vagus.  The 
muscles  are  those  of  respiration  and  of  the  fauces  and 
soft  palate. 

The  various  abnormal  modes  of  respiration  which  occur  in  disease,  may  be 
referred  either  to  altered  rhythm  of  the  centre  (Cheyne  Stokes  breathing),  to 
excessive  proneness  to  the  production  of  reflex  expiratory  action  (spasmodic 
cough),  to  suspension  of  vagiis  action  (true  asthma),  &c. 

Influence  of  the  Nervous  System  on  the  Heart. —  i.  The 


OF   THE   HEART.  85 

regulatory  nervous  system  of  the  heart  consists  of  (a)  the 
intra-cranial  heart-centre  (spinal  accessory  nuclei)  ;  (d)  the 
fibres  of  the  spinal  accessory  and  vagus,  which  are  dis- 
tributed to  the  licart,  and  (c)  the  accelerator  nerves. 
2.  It  was  discovered  by  E.  H.  Weber  in  1842  that  through 
the  vagus  the  brain  exercises  an  inhibitory  influence  on 
the  heart,  />.,  that  excitation  of  the  cardiac  fibres  of  the 
vagus  cither  arrests  the  heart  in  diastole,  or,  if  less  intense, 
diminishes  the  frequency  of  its  beats  by  prolonging  each 
diastolic  interval,  and  thus  diminishes  the  arterial  pressure, 
while  it  increases  the  amplitude  of  the  arterial  pulsation. 
Between  the  excitation  and  the  effect,  a  delay  takes 
place  which  (in  the  rabbit)  amounts  to  ^  second.  3.  The 
effect  above  described  is  produced  reflexly  by  excita- 
tion of  various  afferent  nerves,  c^.,  in  the  mammal  by 
inhalation  of  irritant  substances,  in  the  frog  by  excitation 
of  the  "rami  mesenterici."  4.  It  is  also  produced  by 
direct  excitation  of  the  intra-cranial  centre,  by  compres- 
sion of  the  brain,  by  increase  of  arterial  pressure  in  the 
brain,  or  by  the  circulation  in  that  organ  of  venous  blood. 
5.  In  most  mammalia,  particularly  those  in  which,  as  in 
the  dog,  the  influence  of  the  vagus  centre  on  the  heart  is 
constant,  each  inspiratory  act  is  followed  by  increased 
frequency  of  pulse.  This  may,  with  much  probability,  be 
attributed  to  the  inhibitory  influence  of  the  respiratory 
centre  on  that  of  the  heart. 

In  all  of  these  instances,  the  experimental  proof  that  the  vagus  is  the 
channel  by  which  the  heart  is  acted  on,  is  obtained  by  observing  that  the  effect 
is  no  longer  produced  after  both  vagi  have  been  divided. 

6.  In  the  frog,  section  of  both  vagi  is  almost  without 
effect  on  the  rhythm  of  the  heart,  but  in  the  dog,  it  is 
followed  by  great  increase  of  frequency  and  of  arterial 
pressure.  Neither  of  these  effects  is  obvious  in  the 
rabbit. 

7.  Accelerator  Nerves. — The  increased  frequency  of  the 
heart-beats,  which,  in  all  animals,  is  produced  along  with 


S6  INTRA-CARDIAC   GANGLIA. 

increased  arterial  pressure  by  excitation  of  the  cervical 
part  of  the  spinal  cord,  is  attributable  to  direct  excita- 
tion of  the  accelerator  fibres  it  contains.  Accelerator 
nerves,  i.e.,  nerves  of  which  the  excitation  induces  increased 
frequency  of  action  without  in  any  other  way  affecting 
the  circulation,  reach  the  heart  from  the  spinal  cord 
through  the  sympathetic  system.  In  the  rabbit,  they  ap- 
proach the  heart  through  the  inferior  cervical  ganglion  ;  in 
the  dog  they  are  derived  chiefly  from  the  dorsal  ganglia, 
from  the  ist  to  the  5  th.  In  all  cases  there  is  a  delay 
of  several  seconds  between  the  excitation  and  the  effect. 
When  the  inhibitory  and  accelerator  nerves  of  the  heart 
are  excited  simultaneously,  the  effects  balance  each 
other. 

Infra-cardiac  Ganglia  and  Nerves  of  the  Heart. — The 
nervous  system  of  the  heart  of  the  frog  consists  of  (i)  a 
plexus,  which  is  situated  in  the  septum  between  the 
auricles,  close  to  the  opening  by  which  the  right  auricle 
communicates  with  the  sinus  venosits.  This  is  con- 
nected by  nerve  filaments  with  (2)  smaller  groups  of 
ganglion  cells  (Bidder's  ganglia)  in  the  neighbourhood  of 
the  auriculo-ventricular  furrow.  Collections  of  ganglion 
cells  exist  in  other  parts  of  the  heart,  but  their  arrange- 
ment is  imperfectly  known.  The  phenomena  relating  to 
the  functions  of  the  intra-cardiac  ganglia  may  be  studied 
in  the  heart  after  its  removal  from  the  body,  either  in  the 
empty  state  or  when  supplied  with  blood  or  other  nutrient 
liquid  in  such  a  way  as  to  enable  it  to  fill  and  discharge 
itself  under  natural  conditions.  The  liquid  used  must 
contain  the  salts  of  the  blood,  and  a  trace  of  proteid,  but 
need  not  contain  haemoglobin.  Mechanical  or  electrical 
excitation  of  the  dorsal  surface  of  the  right  auricle 
(inhibitory  centre)  arrests  the  heart  in  diastole.  Accord- 
ingly, if  a  tight  ligature  is  placed  round  the  heart  in 
this  position,  it  loses  the  power  of  rhythmical  contrac- 
tion.    If,  thereupon,  the    auricles   are  cut  off    from    the 


VASCULAR   NERVOUS   SYSTEM.  ^y 

ventricle,  the  rhythmical  action  is  resumed,  provided  that 
the  viiddlc  part  of  the  base  of  the  ventricle  remains 
intact.  So  soon  as  this  part  is  cut  off  or  destroyed,  the 
rhythmical  contractions  cease  ;  it  is  therefore  believed  to 
contain  the  motor  centre  for  the  rhythmical  motion  of  the 
ventricle.  After  its  removal,  the  ventricle  responds  to 
each  single  or  mechanical  excitation  by  a  single  contrac- 
tion, determined  by  the  direct  action  of  the  excitant  on 
the  muscular  fibre.  Similar  motor  centres  are  inferred  to 
exist  in  the  sinus,  auricles,  and  bulb.  Application  to 
the  beating  heart  of  a  trace  of  solution  of  the  alkaloid 
viuscarine,  stops  it  in  diastole.  The  effect  is  promptly 
counteracted  by  the  application  of  solution  of  atropine  in 
similar  manner  and  quantity.  A  heart  so  '  atropinized  ' 
cannot  be  stopped  in  diastole,  either  by  mechanical  or 
electrical  excitation  of  its  inhibitory  centre. 

Ganglia  exist  in  the  hearts  of  the  higher  animals,  but 
nothing  is  known  of  their  functions. 

Influence  of  the  Nervous  System  on  the  blood  vessels 
{ Vascular  Nervous  System).  —  The  principal  vaso-con- 
strictor  centre  is  situated  in  the  upper  part  of  the  floor 
of  the  fourth  ventricle ;  subordinate  centres  exist  in  the 
spinal  cord,  both  in  mammalia  (Strieker)  and  in  the  frog. 
The  channels  of  the  influence  of  these  centres  on  the 
arteries  are  contained  in  the  lateral  columns  of  the  spinal 
cord,  from  which  they  extend  by  the  anterior  roots  and 
rami  communicantes  to  the  ganglia  and  praevertebral 
plexuses  of  the  sympathetic  system,  whence  vaso  con- 
strictor nerves  are  distributed  to  the  arteries. 

The  constrictor  centres  are  in  constant  action  ;  their 
activity  varies  with  the  CO2  tension  of  the  blood,  and  is 
consequently  augmented  by  arrest  of  the  circulation  in  the 
brain.  The  centres  are  also  influenced  by  excitation  of 
sensory  nerves,  of  which  the  ordinary  eftect  is  to  increase 
their  activity.  But  in  the  case  of  the  afferent  fibres  which 
reach  the  vagus  from   the   heart    (Depressor  fibres),  the 


88  VASCULAR   NERVOUS   SYSTEM. 

opposite  effect  is  produced  (see  below).  It  cannot  be 
stated  whether  in  this  case  the  constrictor  centres  are 
acted  upon  directly,  or  with  the  intervention  of  other 
centres,  i.  Section  of  the  spinal  cord  in  the  neck  causes  in 
all  animals  vascular  dilatation  and  consequent  diminution 
of  the  arterial  pressure,  and  of  the  velocity  of  the  circula- 
tion. As  the  dilatation  affects  the  vessels  of  the  viscera 
much  more  than  those  of  the  skin  and  of  the  muscles, 
the  distribution  of  the  blood  is  altered,  2.  Excitation  of 
any  external  sensory  nerve  produces  contraction  of  the 
blood  vessels  of  the  viscera,  but  dilatation  of  those  dis- 
tributed to  the  muscles  and  skin  (Heidenhain,  Bernstein). 
In  the  normal  animal  the  effect  of  these  vascular  changes 
is  to  increase  the  velocity  of  the  circulation  and  the 
arterial  pressure.  In  those  animals  in  which  the  depres- 
sor forms  a  separate  nerve,  excitation  of  the  central  end 
of  that  nerve  produces  dilatation  of  the  visceral  blood 
vessels,  and  consequent  diminution  of  arterial  pressure. 
3.  Severance  of  the  constrictor  nerves  distributed  to 
external  parts,  or  of  spinal  nerves,  produces  relaxation 
of  the  arteries  to  which  they  are  distributed,  but  after  a 
time  the  arterial  tonus  (see  below)  is  restored,  notwith- 
standing that  the  communication  between  the  arteries 
and  the  central  nervous  system  continues  to  be  inter- 
rupted. Excitation  of  the  same  nerves  (peripheral  ends 
after  section)  determines,  tinder  normal  conditions  vas- 
cular constriction,  pallor,  and  diminished  temperature,  in 
the  parts  to  which  they  are  distributed,  and  diminishes 
the  flow  of  blood  in  the  veins  which  lead  from  those  parts. 
If,  however,  the  nerves  subjected  to  excitation  are  in  a 
state  of  partial  degeneration,  consequent  on  previous 
severance,  it  often  happens  that  the  opposite  effects  are 
produced.  Again,  if  the  temperature  of  the  part  is 
already  lower  than  the  normal,  the  vessels  dilate  in 
response  to  the  excitation  instead  of  contracting,  even 
though  the  nerve  excited  may  have  been  divided  imme- 


VASCULAR   NERVOUS  SYSTEM.  89 

diately  before.  4.  Excitation  of  the  nerves  distributed  to 
the  abdominal  viscera  produces,  under  all  circumstances, 
vascular  constriction.  Section  of  the  same  nerves  pro- 
duces as  invsiriably  vascular  dilatation.  5.  In  some 
instances  excitation  of  a  cutaneous  sensory  nerve  leads, 
by  reflex  action,  to  vascular  changes,  limited  to  the  area 
of  its  distribution.  These  reflex  effects  vary  according 
to  the  mode  of  excitation.  6.  Any  nerve  of  which  the 
excitation  (peripheral  end  after  section)  leads  to  vascular 
dilatation  and  hyperaemia  in  the  parts  to  which  it  is  dis- 
tributed, is  called  a  vaso-inJiibitory  nerve.  Fibres  of  this 
kind  are  contained  in  the  lingual  nerve,  some  of  which 
are  distributed  to  the  submaxillary  gland,  others  to  the 
mucous  membrane  of  the  tongue.  All  erectile  organs  are 
provided  with  vaso-inhibitory  nerves,  which  are  distributed 
to  their  arterioles.  On  excitation  of  these  nerves,  whether 
reflex  or  direct,  the  arterioles  expand,  in  consequence  of 
which  the  venous  system  of  the  tissue  becomes  distended 
with  blood.  7.  The  normal  state  of  contraction  of  the 
arteries  of  a  healthy  part  is  called  Tonus.  The  arterial 
tonus  is  maintained  by  the  constant  activity  of  the  vaso- 
constrictor centres ;  it  is  also  influenced  by  conditions 
which  act  independently  of  the  vascular  nervous  system, 
particularly  by  the  temperature  of  the  part  (]\Iosso),  by 
the  pressure  under  which  blood  flows  into  it  (Heiden- 
hain),  by  changes  in  the  structure  of  the  blood  vessels 
(Cohnheim),  &c.  It  is  subject  to  fluctuations  which  recur 
at  irregular  intervals,  and  may  either  be  limited  to  par- 
ticular arteries  or  may  affect  so  large  a  number  simulta- 
neously as  to  produce  variations  of  the  volume  of  the 
organs  supplied  by  them  (INIosso),  or  fluctuations  of  arterial 
pressure  (Traube,  Hering). 

The  regulation  of  the  Circiilation  of  the  blood,  i.e.,  the 
maintenance  of  such  a  relation  between  the  activity  of 
the  heart  and  the  resistance  of  the  blood  vessels  as  is  most 
advantageous,  is  effected  by  the  combined  action  of  the 


90  ASPHYXIA, 

cardiac  and  vascular  centres.  Overaction  of  the  heart  is 
prevented  by  the  influence  of  the  resulting  augmentation 
of  intra-cranial  pressure  on  the  heart  centre  in  the  medulla 
oblongata  ;  over-constriction  of  the  vessels  by  the  influence 
of  the  resulting  increase  of  endocardial  pressure  through 
the  depressor  fibres  of  the  vagus  on  the  vaso-motor 
centre. 

Death  by  Asphyxia. — When  respiration  is  suddenly  pre- 
vented, either  by  complete  occlusion  of  the  air  passages 
or  by  submersion,  the  circulation  of  unarterialized  blood 
in  the  brain  gives  rise  to  disturbances  of  the  actions  of 
the  respiratory,  cardiac,  and  vascular  centres,  which  in  a 
few  minutes  bring  respiration  and  circulation  to  an  end. 
The  process  is  divisible  into  two  stages.  The  first  stage  is 
characterized  by  rapidly  increasing  hyperpnoea,  contraction 
of  the  arteries,  increased  arterial  pressure,  and  acceleration 
of  the  circulation  ;  towards  its  close  the  expiratory  move- 
ments become  more  forcible  than  the  inspiratory,  and  as 
insensibility  approaches,  pass  into  "  expiratory  convul- 
sions "  of  short  duration.  In  the  second  stage  the  animal 
is  entirely  unconscious  ;  the  pupils  are  first  contracted, 
then  dilated,  while  the  convulsive  expirations  give  place  to 
violent  inspiratory  gasps.  After  these  have  ceased  the 
heart  continues  to  beat,  at  first  slowly,  then  with  increased 
frequency  but  diminished  effect,  until  at  last  the  arterial 
pressure  has  sunk  to  zero,  and  the  whole  of  the  blood  has 
collected  in  the  venous  system  and  in  the  cavities  of  the 
heart.  The  duration  of  the  process  is  mainly  dependent 
on  the  quantity  of  air  contained  in  the  respiratory  cavity 
at  the  moment  of  occlusion  of  the  air  passages,  on  the 
relative  quantity  of  blood  which  the  animal  possesses,  on 
its  age,  and  on  the  activity  of  its  chemical  processes. 

Influence  of  the  nervous  system  on  the  Temperature  of  the 
body. — The  influence  of  the  nervous  system  on  the  heat- 
producing  processes,  by  which  the  constancy  of  the  tem- 
perature of  the  body  is  maintained,  is  as  yet  unknown. 


REFLEX   OF  SWALLOWING.  91 

The  discharge  of  heat  is,  in  man,  chiefly  dependent  on  the 
circulation  of  the  blood  in  the  skin  and  subcutaneous 
tissues,  and  on  the  secretion  of  sweat.  Both  of  these  pro- 
cesses are  presided  over  by  nervous  mechanisms  of  such  a 
nature  that  their  activity  varies  with  the  surface  tempera- 
ture of  the  body.  In  animals  (particularly  in  the  dog) 
the  increased'  activity  of  the  respiratory  movements,  which 
is  produced  by  increase  of  bodily  temperature  {see  Influ- 
ence of  Nervous  system  on  respiration),  also  serves  as  an 
efficient  means  of  regulation. 

The  Reflex  process  of  Sivalloiving. — In  the  accomplish- 
ment of  the  act  by  which  food  is  conveyed  from  the  fauces 
into  the  stomach,  the  following  changes  take  place  : — 

The  larynx  is  drawn  upwards  under  the  tongue  and 
nearer  to  the  hyoid  bone,  the  epiglottis  applying  its  upper 
surface  to  the  base  of  the  tongue,  and  its  under  surface  to 
the  larynx  ;  the  glottis  is  closed  ;  the  palato-pharyngeal 
arches  tighten  and  approach  each  other,  without  quite 
meeting.  The  soft  palate  with  the  uvula  is  drawn  back- 
wards (by  the  combined  action  of  the  levatores  and  palato- 
pharyngei),  while  the  posterior  wall  of  the  pharynx 
advances  to  meet  it,  and  thus  completely  shuts  off  the 
nares  from  the  pharynx.  The  morsel  as  it  glides  down- 
wards between  the  nearly  even  surfaces  offered  by  the 
tongue,  epiglottis  and  cricoid  cartilages  in  front,  and  the 
palato-pharyngeal  arches  behind,  is  at  once  seized  by  the 
constrictors  and  carried  onwards  by  their  successive  con- 
tractions into  the  oesophagus.  By  a  mode  of  action  which 
is  called  "peristaltic,"  and  which  resembles  that  of  the 
intestine  and  other  muscular  tubes,  the  food  is  conveyed 
as  far  as  the  closed  sphincter  of  the  stomach.  As  soon  as 
this  happens,  the  sphincter  opens  to  allow  of  its  entrance 
into  the  stomach,  closing  again  immediately. 

The  centre  which  presides  over  this  reflex  process  has  its 
seat  in  the  medulla  oblongata.  It  derives  its  most  impor- 
tant afferent  influences  from  the  mucous  membrane  of  the 


92  PERISTALTIC    ACTION, 

fauces.  After  section  of  the  vagus,  near  its  origin  (vago- 
accessorius),  the  muscles  of  the  pharynx,  as  well  as  those 
of  the  larynx  and  the  oesophagus,  are  inactive,  and  the 
reflex  act  of  deglutition  is  prevented.  The  effect  of 
removal  of  the  accessorius  roots  is  scarcely  different. 
After  section  of  both  vagi  in  the  neck,  the  first  part  of  the 
process  is  possible,  but  it  cannot  be  completed.  Food 
collects  in  the  relaxed  oesophagus,  being  prevented  from 
entering  the  stomach  by  the  permanently  closed  cardia ; 
the  glottis  being  inactive,  portions  of  food  are  apt  to  enter 
the  trachea.  The  peristaltic  action  of  the  oesophagus 
differs  from  that  of  the  intestine  in  being  much  more 
dependent  on  the  intra-cranial  centre  which  governs  it. 

Regulation  of  the  peristaltic  action  of  the  Stomach  and 
Intestine. — Throughout  the  alimentary  canal  the  motions 
of  its  contents  are  produced  by  temporary  constrictions  of 
its  wall,  which  progress  in  the  direction  of  its  length.  In 
the  intestine  all  that  is  observed  is  that  the  constriction 
folloivs  the  mass  in  its  progress  and  that,  as  a  rule,  every 
peristaltic  act  begins  at  the  pylorus  and  advances  onwards. 
In  the  stomach,  the  action  is  similar,  but  in  consequence 
of  the  form  of  the  cavity,  the  effect  is  different  ;  for  the 
contents,  instead  of  advancing,  circulate  along  the  smaller 
curvature  from  pylorus  to  cardia,  and  along  the  larger,  in 
the  opposite  direction.  In  the  inactive  state,  the  stomach 
is  contracted  and  the  pylorus  closed,  whereas  the  intestine 
is  (apparently)  relaxed.  When  food  is  introduced  into 
the  stomach  its  wall  begins  to  relax  and  contract  alter- 
nately, each  change  beginning  at  the  cardia.  These 
movements,  at  first  feeble,  become  more  and  more 
active  towards  the  close  of  the  process  of  gastric  diges- 
tion, the  pylorus  opening  more  and  more  at  each  relaxa- 
tion, so  as  to  allow  of  the  gradual  escape  of  chyme  into 
the  duodenum. 

The  motions  of  the  stomach  are  in  large  measure  influ- 
enced  by  the  vagus,   for  after  section  of  both  vagi  the 


REFLEX   OF  VOMITING.  93 

stomach  is  almost  inactive,  but  can  be  brought  into  action 
by  exciting  the  nerve.  In  the  frog,  after  section  of  both 
vagi,  the  stomach  is  contracted.  The  function  of  the  vagus 
in  relation  to  the  stomach  is  therefore  regarded  as  inhi- 
bitory. 

The  peristaltic  motion  of  the  intestine  is  increased  in 
dyspncea,  arrested  in  apnoea.  Arrest  of  the  circulation 
usually  increases  its  activity,  but  the  effect  varies  according 
to  the  previous  state  of  the  intestine.  The  splanchnic 
nerves  are  the  channels  by  which  the  influence  of  the 
cerebro-spinal  centres  is  conveyed  to  the  intestines,  but 
nothing  can  be  certainly  stated  as  to  the  nature  of  that 
influence.  Inasmuch  as  the  peristaltic  motion  can  be 
always  suspended,  if  previously  active,  by  excitation  of 
these  nerves,  an  inhibitory  function,  like  that  of  the  vagus 
in  relation  to  the  stomach,  is  attributed  to  them. 

The  Reflex  of  Vomiting. — Vomiting  consists  of  three 
acts,  viz.  (i)  Descent  of  the  diaphragm,  (2)  Relaxation  of 
the  cardia  and  contraction  of  the  longitudinal  fibres  of 
the  cardiac  end  of  the  oesophagus,  (3)  Closure  of  the 
glottis  and  compression  of  the  stomach  between  the 
abdominal  muscles  and  the  still  contracted  diaphragm, 
and  discharge  of  its  contents  by  a  mode  of  action  of  the 
muscles  of  the  oesophagus  and  pharynx,  which  resembles 
that  of  swallowing  but  is  in  reversed  order.  Usually  the 
process  is  preceded  by  increased  secretion  of  saliva, 
which  is  immediately  swallowed.  At  the  moment  of  the 
discharge  of  the  contents  of  the  stomach  the  muscles  of 
the  pharynx  are  brought  into  action,  so  as  to  give  to 
that  cavity  the  same  form  as  in  swallowing,  and  prevent 
the  passage  of  vomited  matters  into  the  larynx  or  nares  : 
the  neck  is  also  extended.  The  centre  for  vomiting  is 
in  the  medulla  oblongata,  and  is  in  close  relation  with 
those  which  preside  over  the  reflexes  of  coughing  and 
swallowing.  It  may  be  induced  either  reflexly  or  by 
direct  action  on  the  centre.     In  the  latter  case,  retching 


94  INFLUENCE   OF   NERVOUS   SYSTEM 

may  occur  even  after  section  of  both  vagi,  but  effectual 
vomiting  is  impossible. 

The  Reflex  of  Defcecation. — As  defsecation  is  possible 
after  severance  of  the  spinal  cord  in  the  dorsal  region,  pro- 
vided that  the  lumbar  part  of  the  cord  is  in  a  normal  state, 
it  must  be  essentially  a  reflex  process,  governed  by  a  spinal 
centre.  When  accomplished  under  these  conditions,  it 
consists  of  two  acts,  namely,  peristaltic  contraction  of  the 
rectum  and  relaxation  of  the  sphincter  externus.  The 
mode  of  action  of  the  latter,  although  it  consists  of  striped 
fibres,  resembles,  when  not  controlled  by  the  will,  that  of 
the  cardia  and  pylorus  :  in  its  ordinary  state  it  is  con- 
tracted, but  it  is  excited  to  rhythmical  relaxation  by  the 
presence  of  faecal  matter  in  the  neighbouring  part  of  the 
rectum. 

The  Reflex  of  Micturition. — The  retention  and  discharge 
of  urine  are  also  reflex  acts,  not  necessarily  dependent  on 
the  will.  The  mechanism  of  micturition  resembles,  so  far 
as  the  bladder  is  concerned,  that  of  defsecation,  urine  being 
discharged  after  severance  of  the  spinal  cord,  at  long  inter- 
vals, by  the  simultaneous  contraction  of  the  muscular  wall 
of  the  bladder  and  relaxation  of  the  sphincter,  this  pri- 
mary act  being  accompanied  by  other  auxiliary  movements 
accomplished  by  striped  muscles  acting  under  the  direction 
of  the  same  centre.  In  the  normal  animal,  the  anal  and 
vesical  sphincters  are  so  far  under  the  control  of  the  will 
that  their  relaxation  can  be  inhibited  by  voluntary  effort. 

hifliience  of  the  nervous  system  on  the  processes  of  Secre- 
fion. — The  processes  of  secretion  which  have  been  hitherto 
investigated,  are  those  of  the  salivary  glands,  the  pancreas, 
the  gastric  glands,  the  liver  and  the  kidney. 

The  salivary  glands  are  normally  inactive,  excepting 
when  excited  by  the  presence  of  sapid  substances  in  the 
mouth.  Hence  the  process  is  a  reflex  one.  The  centre 
which  governs  it  is  in  the  medulla  oblongata,  and  transmits 
its   influence  to  the  submaxillary  gland  by  the   chorda 


ON   SECRETION.  95 

tympani,  and  to  the  parotid  by  a  nerve  which  springs 
directly  from  the  auriculo-temporal,  ultimately,  like  the 
chorda,  from  the  facial.  The  submaxillary  may  be  excited 
to  normal  action  by  direct  faradization  of  the  chorda,  in 
which  case  it  pours  out  its  secretion  in  abundance,  and 
with  such  force,  that  if  its  duct  is  occluded,  its  internal 
surface  is  exposed  to  a  pressure  which  may  exceed  the 
arterial.  In  addition  to  this,  excitation  of  the  chorda 
produces  dilatation  of  the  arteries  of  the  gland,  in  conse- 
quence of  which  its  supply  of  blood  is  largely  increased. 
It  can,  however,  be  shown  that  each  of  these  two  effects  is 
independent  of  the  other.  During  excitation,  the  tem- 
perature of  the  gland  rises  and  the  secreting  cells  undergo 
important  changes  (in  the  dog,  disappearance  of  the 
"  mucous  cells "  or  discharge  of  their  contents,  multi- 
plication or  regeneration  of  the  "  protoplasm-cells "). 
The  submaxillary  gland  can  also  be  made  to  secrete  by 
excitation  of  the  vaso-constrictor  nerves  which  accompany 
its  arteries ;  the  product  so  obtained  is  of  high  specific 
gravity  and  contains  much  mucus.  Severance  of  all  the 
nerves  of  the  gland  produces  a  continuous  discharge  of 
watery  liquid  which  continues  for  some  time. 

The  pa7icreas.  During  the  intervals  of  digestion  the 
pancreas  is  inactive.  It  begins  to  secrete  immediately 
after  food  is  taken  and  attains  its  greatest  activity  towards 
the  end  of  gastric  digestion.  At  this  time  it  is  red  and 
turgid,  and  is  richest  in  the  material  to  which  its  secretion 
owes  its  digestive  activity  ;  its  cells  are  larger  than  before 
and  contain  a  granular  material,  which  as  secretion  goes 
on  disappears,  but  is  subsequently  regenerated.  Nothing 
is  known  as  to  the  channels  by  which  the  nervous  system 
influences  the  process. — The  gastric  glands  are  normally 
brought  into  activity  by  the  presence  of  food  or  of  saliva 
in  the  stomach.  Their  secretion  ceases  when  the  stomach 
is  empty,  but  can  be  readily  excited  by  mechanical  and 
chemical  stimuli,  particularly  by  alkaline  liquids.     It  is 


96  [nerves  of  liver  and  kidney. 

not  dependent  on  integrity  of  the  vagus  nerves.  Its 
activity  is  associated  with  increased  circulation  of  blood 
in  the  mucous  membrane,  and  with  changes  in  the  secret- 
ing cells,  comparable  with  those  already  described  in 
other  glands.  Nothing  can,  however,  as  yet  be  stated 
with  certainty  as  to  the  relation  of  these  changes  with 
the  process. 

The  liver. — The  secretion  of  bile  cannot'  be  directly 
excited  by  any  mode  of  acting  on  the  nervous  system. 
Excitation  of  the  spinal  cord,  which  at  first  increases  the 
discharge  of  bile,  by  producing  constriction  of  the  bile- 
ducts,  eventually  diminishes  it.  The  secretion  of  bile  is 
arrested  by  even  very  slight  increase  of  pressure  in  the 
bile  ducts ;  whenever  this  happens  bilin  and  colouring 
matter  exist  in  the  circulating  blood  (jaundice).  The 
power  of  the  liver  cells  to  store  glycogen  is  annulled  by 
destruction  either  of  the  centre  which  controls  its  blood- 
vessels or  of  the  channels  by  which  that  control  is  exer- 
cised ;  in  either  case  the  urine  becomes  saccharine  (glyco- 
suria). A  similar  effect  is  produced  by  curare,  carbonic 
oxide  and  some  other  poisons,  as  well  as  by  central  exci- 
tation of  the  vagus. 

The  kidneys  possess  no  secreting  nerves :  the  renal 
nerves  have  no  other  function  excepting  that  of  constric- 
tors of  the  arteries.  The  rate  of  secretion  of  urine  is 
directly  influenced  by  the  state  of  the  circulation :  thus, 
it  can  be  increased  in  animals  by  augmentation,  and 
diminished  by  reduction,  of  the  pressure  under  which 
blood  enters  the  glomeruli.  It  can  be  diminished  or  even 
arrested  by  increasing  the  pressure  in  the  renal  veins. 
By  destruction  of  the  renal  vascular  centre  in  the  floor  of 
the  fourth  ventricle,  or  of  the  renal  nerves,  the  vascular 
tone  of  the  kidneys  is  annulled,  in  consequence  of  which 
the  urine  flows  abundantly  (polyuria)  and  often  contains 
albumin  (albuminuria),  but  is  not  necessarily  saccharine. 
Similar  effects  are  observed   after  severance  of  the  renal 


MAINTENANCE   OF    BALANCE.  9/ 

nerves ;  excitation  of  tlic  renal  nerves  arrests  the  secre- 
tion. 

Ri'^n/atioii  of  Locovwtion  {Maintenance  of  Balance). — 
The  motions  of  the  body  in  walking  and  other  modes  of 
progression,  although  under  the  influence  of  the  will,  are 
regulated  by  centres  which  act  in  obedience  to  impressions 
of  which  the  will  takes  no  cognizance,  received  from  the 
retinae,  from  the  semi-circular  canals,  and  other  sensory 
end-organs.  These  impressions  have  to  do  chiefly  either 
with  the  relation  of  the  head  to  the  plummet  line,  or  to 
changes  of  speed  or  direction  in  the  motions  of  the  head 
or  body.  "With  reference  to  impressions  of  the  latter 
class,  it  is  to  be  noted,  that  all  felt  motions  give  rise,  on 
their  cessation,  to  a  subjective  sensation  of  motion  in  the 
opposite  direction. 

After  injury  of  either  of  the  crura-cerebri,  animals  have 
a  tendency  to  rotation  of  the  body  round  an  axis,  which 
usually  lies  on  the  side  of  the  body  opposite  to  that  in- 
jured. This  tendency,  when  strong,  manifests  itself  in 
rolling  ;  when  weaker,  in  viam^gc  motion.  Similar  efi'ects 
follow  injury  of  the  cerebellum,  but  in  this  case  the  axis 
of  rotation  is  often  on  the  same  side  of  the  body  as  the 
injury.  After  injury,  or  irritation  of  the  semi-circular 
canals,  birds  walk  as  if  they  had  lost  their  balance,  and 
the  head  oscillates.  The  oscillation  varies  in  direction 
according  as  the  vertical  or  horizontal  canals  are  inter- 
fered with  :  if  the  former,  the  head  moves  backwards  and 
forwards  ;  if  the  latter,  it  is  rotated  from  side  to  side.  At 
the  same  time,  the  head  assumes  an  unnatural  attitude, 
and  the  body  tends  to  fall  backward  or  to  the  side.  The 
sensation  of  vertigo,  in  which  the  body  of  the  affected 
person  seems  to  rotate  round  its  vertical  axis,  is  produced 
by  passive  rotation  in  the  opposite  direction  :  when  in- 
tense, it  expresses  itself  in  actual  rotation,  the  direction 
of  which  is  always  opposed  to  that  of  the  subjective 
motion.     Vertigo   may  be  also  produced    by  the  passage 

H 


98  MOTIONS   OF   THE  EYEBALLS. 

of  a  voltaic  current  through  the  brain  (cerebellum  ?),  in 
which  case  the  direction  of  the  subjective  rotation  is 
determined  by  that  of  the  current.  Both  kinds  of  vertigo 
are  accompanied  by  nystagmus.  In  the  frog,  after 
removal  of  the  hemispheres,  locomotion  is  as  perfect  as 
in  the  normal  animal,  provided  that  the  optic  lobes  and 
cerebellum  are  present.  A  frog  which  possesses  its  cere- 
bellum, but  has  no  optic  lobes,  jumps  normally,  but  fails 
in  maintaining  its  balance.  In  mammalia  (the  dog),  loss 
of  the  cerebellum  is  followed  by  disorders  and  perverted 
action  of  the  muscles  of  the  trunk  and  limbs,  in  con- 
sequence of  which,  neither  voluntary  nor  reflex  acts 
can  be  accomplished  in  a  manner  adapted  to  their  pur- 
pose. 

All  of  these  phenomena  may  be  understood  on  the 
supposition  that  centres  exist  (in  the  cerebellum  i^)  of 
of  which  it  is  the  function  (i)  to  receive  impressions  as 
to  the  direction  of  the  passive  and  active  motions  of  the 
body  and  of  its  parts  ;  and  (2)  to  direct  and  regulate  the 
actions  of  the  muscles  of  the  trunk  and  limbs  (indepen- 
dently of  consciousness)  in  obedience  to  those  impres- 
sions. 

Regulation  of  the  Motions  of  the  Eyeballs  and  the 
Actions  of  the  Iris  and  Tensor  of  the  Choroid. — These 
actions  are  governed  by  centres  which  have  their  seat  in 
the  floor  of  the  aqueduct  of  Sylvius,  and  of  the  3rd  and 
4th  ventricles,  the  influence  of  which  is  conveyed  to  the 
muscular  structures,  over  which  they  preside,  by  the  3rd, 
4th,  and  6th  nerves,  as  well  as  by  channels  which  are  con- 
tained in  the  cervical  portion  of  the  spinal  cord,  and  in 
the  corresponding  part  of  the  sympathetic  system.  They 
have  been  localized  by  experiment  as  follows : — Excita- 
tion of  the  floor  of  the  aqueduct  at  its  entrance  into  the 
third  ventricle,  produces  convergence  of  the  visual  axis, 
and  contraction  of  the  pupil  ;  excitation  of  the  anterior 
tubercles  of  the  corpora  quadrigemina,   or  of  the  optic 


ACTIONS   OF   THE   IRIS.  93 

thalami,  occasions  divergence  and  dilatation  ;  on  excita- 
tion of  the  outer  part  of  either  anterior  tubercle,  both 
eyeballs  are  rotated  to  the  opposite  side. 

The  iris  receives,  in  addition  to  sensory  and  vascular 
nerves,  constrictor  nerves,  which  are  distributed  to  the 
sphincter  pupillae,  and  dilatator  fibres,  which  are  believed 
to  terminate  in  muscular  structures  of  corresponding 
function.  Every  excitation  of  the  retina  by  light  is  fol- 
lowed, after  an  interval  of  about  half  a  second,  by  con- 
traction of  the  pupils.  Both  pupils  respond  to  excitation 
of  one  retina.  In  the  frog,  the  iris  continues  to  respond 
to  excitation  of  the  retina,  even  after  the  eye  has  been 
removed  from  the  body.  In  accommodation  for  near 
vision,  the  contraction  of  the  tensor  choroidea;  is  normally 
associated  with  convergence  of  the  visual  axes  and  nar- 
rowing of  the  pupil.  The  dilatator  nerves  of  the  iris  are 
derived  immediately  from  the  trigeminus,  ultimately  from 
the  sympathetic  system,  for  excitation  of  the  upper  cer- 
vical ganglion  produces  dilatation,  and  destruction  of  it 
narrowing  of  the  pupil.  Dilatation  is  also  produced  re- 
flexly  by  excitation  of  any  sensory  nerve :  in  all  cases  it 
is  associated  with  vascular  contraction  (sec  Vascular  Ner- 
vous System),  proptosis,  widely-opened  eyelids,  and  re- 
traction of  the  membrana  nictitans.  These  effects  are* 
weakened,  but  not  annulled,  by  extirpation  of  the  upper 
ganglion  of  the  sympathetic.  Corresponding  phenomena 
are  observed  in  dyspnoea  and  during  violent  muscular 
efforts.  In  deep  sleep,  the  visual  axes  converge,  and  the 
pupil  is  contracted.  Certain  alkaloids  (called  mydriatics) 
produce  lasting  dilatation  of  the  pupil,  associated  with 
complete  relaxation  of  the  tensor  of  the  choroid.  Others 
(called  myotics)  have  the  opposite  effect  ;  in  the  former 
case,  the  action  is  known  to  have  its  seat  in  the  eyeball 
itself  Convergence  of  the  visual  axes,  and  narrowing  of 
the  pupil  are  so  associated,  that  one  of  them  cannot  be 
normally  accomplished  without  the  other.     Accordingly, 

H    2 


lOO  FUNCTIONS   OF   THE   BRAIN. 

accommodation  for  near  vision  is  always  accompanied  by 
contraction  of  the  irides. 

Regulation  of  the  Movements  of  Expression. — On  this 
subject,  information  is  derived  from  the  observation  of 
disease.  When  the  muscles  of  one  side  of  the  face 
are  rendered  temporarily  or  permanently  inactive  by  com- 
pression or  destruction  of  \heportio  dura  in  the  Fallopian 
canal,  the  affected  side  loses  its  expression,  and  is  drawn 
to  the  opposite  side.  The  affected  cheek  is  flabby,  and 
the  eyelids  cannot  be  closed  ilagophthahmis  paralyticus), 
in  consequence  of  which,  tears  flow  over  the  cheek,  while 
the  exposed  eyeball  is  rotated  upwards.  If  the  lesion  is 
on  the  central  side  of  the  genu,  these  phenomena  are 
accompanied  by  asymmetry  of  the  posterior  arch  of  the 
fauces,  consequent  on  inactivity  of  the  levator  palati,  as 
well  as  by  loss  or  impairment  of  hearing ;  moreover,  the 
salivary  glands  of  the  affected  side  cannot  be  excited  to 
reflex  secretion. 

The  Functions  of  tJie  Brain — comprising  those  of  the  Cor- 
tical Convolutions,  Corpora  Striata,  and  Optic  TJialami. — A 
frog  which  has  been  deprived  of  its  hemispheres,  acts  in  all 
respects  as  a  normal  frog,  excepting  that  it  is  incapable  either 
of  interpreting  its  sensations,  or  of  initiating  voluntary  acts. 
The  condition  of  the  brainless  mammalian  animal  is 
analogous.  It  is  subject  to  emotion,  and  acts  in  such  a 
way  as  to  show  that  it  is  influenced  both  by  impressions 
received  through  the  nerves  of  common  sensation  and 
through  those  of  sight  and  hearing,  but  it  is  incapable  of 
understanding,  remembering,  or  willing.  All  of  its  acts 
are  of  the  kind  described  on  p.  78.  Any  direct  inter- 
ference with  the  brain  as,  eg.,  by  compression  of  its  sub- 
stance, or  by  arrest,  or  great  diminution  of  its  circulation 
(as  in  syncope),  annuls  consciousness. — Although  at  first 
sight  the  development  of  the  hemispheres  seems  in  animals 
to  exhibit  only  a  very  general  relation  to  that  of  the 
mental  faculties,  it  can  be  shown  that  the  relation  between 


THE  CONVOLUTIONS.  lOI 

the  wciy^ht  of  the  brain  and  intelligence  is  a  very  close 
one,  provided  that  the  weight  of  the  mesencephalon  be 
taken  as  the  standard  of  comparison,  not  that  of  the 
whole  botly. 

The  inference  that  is  suggested  by  the  anatomical  rela- 
tions of  the  corpora  striata,  viz.,  that  they  serve  to  bring 
into  connection  the  cortex  of  the  hemispheres,  particularly 
of  the  "  motor  region,"  with  the  reflex  motor  centres  of 
the  mid-brain,  is  supported  by  clinical  observations,  for 
the  almost  constant  result  of  lesions  of  these  organs  is 
loss  of  voluntary  control  over  the  muscles  of  the  opposite 
side  of  the  body  (hemiplegia),  a  condition  which  is  not, 
as  a  rule,  permanent.  By  experiment,  we  learn  that  the 
part  of  the  corpus  striatum  on  which  this  effect  depends, 
is  the  nucleus  Icuticularis,  for  while  destruction  of  this 
part  produces  as  complete  hemiplegia  as  if  the  whole 
hemisphere  were  removed,  interference  with  the  nucleus 
caudatus  is  almost  without  effect. 

There  is,  at  present,  no  evidence  either  that  the  corpora 
striata  contain  motor  centres,  or  the  contrary.  As  regards 
the  functions  of  the  optic  thalamus,  no  general  statement 
can  at  present  be  made. 

The  Convolutions. —  It  was  formerly  believed  that  all 
parts  of  the  cortex  of  the  hemispheres  have  the  same 
function.  It  is  now  known  that  in  certain  regions  each 
part  has  physiological  relations  which  are  peculiar  to 
itself.  The  proof  that  this  is  so,  lies  in  the  observation 
of  two  classes  of  phenomena,  viz.,  (i)  the  effects  of 
electrical  excitation  of  particular  parts  of  the  surface  of 
the  hemispheres,  and  (2)  the  results  of  ablation  of  certain 
parts. 

As  regards  the  effects  of  excitation,  the  best  ascer- 
tained facts  are  those  which  relate  to  the  excitation  of 
the  pr?e-frontal,  post-frontal,  and  super-sylvian  convolutions 
of  the  dog ;  corresponding  in  position  to  the  convolutions 
which  surround    the    fissure   of  Rolando    in    the  human 


102  THE   CONVOLUTIONS. 

brain.  These  excitations  severally  induce  co-ordinated 
motions  (varying  in  their  character  according  to  the  pre- 
cise part  excited)  of  the  head  and  neck,  of  the  extremi- 
ties, and  of  the  muscles  of  the  face,  on  the  side  of  the 
body  opposite  that  on  which  the  cerebral  surface  is  ex- 
cited. After  removal  or  destruction  of  any  of  these  parts 
of  the  cortex,  excitation  of  the  white  substance  sub- 
jacent to  it  produces  the  same  effect  as  excitation  of  the 
part  of  the  cortex  with  which  its  fibres  were  previously 
in  relation,  so  that  the  cortical  substance  is  not  essential. 
In  all  cases,  a  perceptible  interval  of  time  intervenes 
between  the  excitation  and  the  muscular  action  which 
results  from  it. 

The  effects  of  ablation  can  only  be  studied  after  the 
animal  has  entirely  recovered  from  the  immediate  patho- 
logical effects  of  the  injury.  From  observations  so  made, 
we  learn  (i)  that  absence  of  parts  of  the  cortex,  by  the 
excitation  of  which  particular  groups  of  muscles  are 
brought  into  action,  is  not  associated  with  any  impair- 
ment of  the  function  of  the  muscles,  but  only  with  loss  or 
impairment  of  the  power  of  the  animal  to  employ  them 
n  the  performance  of  certain  combined  motions  ;  (2)  that 
destruction  of  the  whole  or  the  greater  part  of  the  cortex 
is  attended  with  impairment  of  memory  and  perception. 
If  the  lesion  is  on  one  side  only,  this  impairment  mani- 
fests itself  chiefly  in  relation  to  impressions  received  from 
the  opposite  side  of  the  body.  According  to  recent 
observations  of  Prof.  H.  Munk,  visual  perception  is 
localized  in  the  occipital  lobe.  Thus  (in  the  dog)  ablation 
of  the  posterior  extremity  of  this  lobe  on  one  side,  pro- 
duces blindness  of  the  middle  and  inner  part  of  the  retina 
of  the  opposite  side,  and  of  the  outer  part  of  the  retina 
of  the  same  side.  In  the  ape,  the  same  lesion  produces 
blindness  of  the  inner  half  of  the  opposite  retina,  and  of 
the  outer  half  of  the  retina  of  the  same  side. — It  has 
been  long  known  clinically,  that  destruction  (by  disease) 


FUNCTIONS   OF   SENSORY  ORGANS.  I03 

of  the  lower  end  of  the  ascending  frontal  convolution  in 
man  (Broca's  convolution),  is  associated  with  aphasia,  a 
condition  in  which  the  patient,  though  able  to  articulate, 
and  possessing  the  power  of  forming  adequate  concep- 
tions which  he  remembers,  is  unable  to  word  them.  In 
the  vast  majority  of  the  cases  in  which  this  happens,  the 
lesion  is  on  the  left  side  of  the  brain. 


Common  and  Special  Sensation. 

{Functions  of  Sensory  end-organs) 

Sensations  and  Perceptions  in  general. — By  the  word 
Sensation  is  meant  in  physiology  the  felt  effect  of  an 
excitation  either  of  a  sensory  end-organ,  or  of  a  sensory 
nerve.  Sensations  which  originate  from  end-organs  are 
divided  into  those  of  common  sensation,  vision,  hearing, 
taste,  &c.,  according  to  the  end-organ  affected.  Sensations 
which  spring  from  direct  irritation  of  sensory  nerves,  are 
usually  painful.  Very  feeble  excitation  of  an  end-organ 
is  not  felt.  As  regards  those  excitations  which  from  their 
nature  admit  of  measurement,  it  was  found  by  E.  H. 
Weber  that  the  degree  of  intensity  which  must  be  attained 
by  any  excitation  in  order  to  be  felt — the  limen  {Rciz- 
schwelle)  is  constant  in  the  same  individual.  As  regards  all 
excitations  of  which  the  intensity  exceeds  the  limen,  it  is 
found  that  the  "  sensible  increment "  {i.e.  the  smallest 
additional  excitation  that  can  be  felt),  is  proportional  to 
the  previous  excitation.  Hence,  the  sensation  produced 
by  any  given  excitation  varies  inversely  as  the  intensity  of 
the  previous  excitation.  The  ratio  of  the  "  sensible  incre- 
ment "  to  the  "  previous  excitation "  differs  in  different 
cases.  Thus  as  regards  light,  it  is  as  i  :  100,  or  there- 
abouts ;  as  regards  sound  as  i  :  3,  and  so  on. 


104  TACTILE   SENSATION. 

Between  an  excitation  of  any  end-organ  and  a  voluntary 
motion  prompted  by  it,  a  time  elapses,  usually  called  the 
"personal  time,"  which  is  made  up  of  the  time  required 
for  recognizing  the  sensation  (perception)  and  the  time 
required  for  transforming  it  into  muscular  action  (intention). 
In  the  simplest  possible  case,  that  in  which  the  person 
under  observation  signifies  his  recognition  of  an  expected 
excitation  by  a  preconcerted  signal,  the  personal  time  is 
about  one-sixth  of  a  second  for  sound,  light,  and  touch. 
By  increasing  the  intensity  of  the  excitation  the  time  may 
be  somcAvhat  diminished.  If  the  sensation  is  of  such  a 
character  as  to  require  interpretation  or  discrimination 
before  it  is  acted  upon,  the  time  is  longer. 


Tactile  Sensation. 

Tactile  sensation  is  regarded  as  the  function  of  the 
so-called  "tactile  corpuscles  "  of  the  skin,  and  of  analogous 
end-organs  which  exist  in  the  exposed  mucous  membranes. 
According  to  the  mode  in  which  the  end-organs  are 
affected,  tactile  sensation  is  divisible  into  that  of  Pressure, 
that  of  Temperature,  and  that  of  Locality.  As  regards 
pressure,  Weber  found  that  an  increment  of  pressure  on 
the  hand  must  amount  to  at  least  one-thirtieth  of  the 
previous  pressure  to  be  felt.  As  regards  temperature,  the 
degree  of  excitation  is  estimated  by  the  difference  between 
the  temperature  of  the  object  applied,  and  the  actual 
temperature  of  the  skin.  A  difference  of  about  one-eighth 
of  a  degree  can  be  felt.  The  sensation  of  locality  may  be 
tested  either  by  "interrogation,"  or  by  measuring  the  dis- 
tance at  which  two  points  of  excitation  must  be  apart  in 
order  that  they  may  be  felt  as  two.  In  relation  to  the 
latter  method,  any  area  on  the  surface  of  the  skin  within 
which  two  such  points  cannot  be  distinguished,  is  called  a 
"sensation    area."      The   v/idths    of    sensation  areas   for 


VISION.  105 

different  regions  arc,  in  millimeters,  as  follows  : — Tongue  i  ; 
finger-tip  2  ;  lip  4  ;  neck  20  ;  back  60. 


Muscular  Sensation. 

Muscular  exertion  is  attended  with  a  "sensation  of 
effort,"  the  relation  of  which  to  the  work  done  {e.g.  the 
weight  lifted),  according  to  Weber's  experiments,  is  such, 
that  no  difference  less  than  a  fortieth  between  two  weights 
lifted  in  succession  can  be  appreciated.  The  sensation  of 
effort  is  therefore  more  delicate  than  the  sensation  of 
pressure.  The  existence  of  sensory  nerve-endings  in  the 
sartorius  muscle  of  the  frog  has  lately  been  demonstrated  ; 
with  this  exception,  channels  of  muscular  sensation  have 
not  hitherto  been  recognized. 


Vision. 

The  Eye  as  an  optical  instrument. — To  understand  the 
paths  of  luminous  rays  through  the  eye  to  the  retina,  it  is 
necessary  to  know  the  form  of  its  three  principal  refracting 
surfaces,  and  the  refractive  indices  of  its  transparent 
media.  Of  the  normal  eye  the  radii  of  curvature,  indices 
of  refraction,  and  dimensions  are  approximately  as  follows  : 
— Radius  of  the  corneal  surface,  8  millimeters,  radius  of 
the  anterior  surface  of  lens,  10  millimeters,  of  posterior 
surface,  6  millimeters,  these  surfaces  being  severally  4 
millimeters  apart  in  the  axis  of  the  eye  ;  the  distance  from 
the  posterior  surface  to  the  retina  is  13  millimeters.  The 
index  of  refraction  of  the  aqueous  or  vitreous  humour  is 
r35,  that  of  water  being  1*336.  The  refraction-index  of 
the  lens  varies  from  i'405  at  the  surface  to  i"454  iii  the 
centre. 

An  eye  supposed  to  be  constructed  according  to  these 
measurements  is  denoted   by  the  term  "schematic  eye," 


I06  THE   REDUCED   EYE. 

which  represents  what  the  normal  eye  would  be,  if  its 
refracting  surfaces  were  spherical,  their  centres  in  the  same 
axis,  and  its  transparent  media  homogeneous. 

The  lensless  or  reduced  Eye. — If  it  were  not  necessary  that 
the  eye  should  be  capable  of  being  adjusted  for  the  distinct 
vision  of  objects  of  different  distances,  the  lens  would  not 
be  required  ;  for  an  eye  which  consists  of  but  one  medium, 
and  has  but  one  refracting  surface,  answers  the  dioptrical 
purposes  of  the  real  eye  in  every  respect,  excepting  that  it 
cannot  be  "accommodated."  A  schema  of  this  kind  is 
called  a  "  reduced  eye."  In  such  an  eye,  if  the  radius  of 
curvature  of  the  cornea  is  5  "12,  and  the  index  of  refraction 
about  I  "3  5,  the  conditions  approach  pretty  closely  to  those 
of  the  normal  eye.  In  the  reduced  eye  the  straight  line 
which  passes  through  the  centre  of  the  cornea  and  the 
centre  of  its  sphere  of  curvature  is  the  axis.  Rays  which 
are  in  the  same  line  with  a  radius  of  the  refracting  surface 
are  not  refracted  :  such  rays  are  called  principal  rays.  As 
they  all  pass  through  the  centre  of  the  sphere  of  curvature 
of  the  cornea,  that  centre  is  called  the  "  crossing  point." 
In  the  normal  eye  this  point  lies  immediately  in  front  of 
the  posterior  surface  of  the  lens.  Any  number  of  rays 
reaching  the  cornea  from  a  luminous  point  (object)  at 
sufficient  distance  in  the  axis,  are  so  refracted  at  the  surface 
that  they  converge  to  a  point  (image)  on  the  other  side. 
Rays  which  emanate  from  a  luminous  point  in  a  plane 
including  the  first,  which  is  vertical  to  the  axis  (object- 
plane)  converge  to  a  point  in  the  same  vertical  plane  with 
the  image  of  the  first  point  (image-plane).  It  thus  happens 
that  (as  regards  flat  surfaces  of  small  extent  which  face 
the  cornea)  every  point  of  the  object-plane  is  focussed  in 
the  image-plane,  forming  there  an  inverted  image.  The 
further  the  object-plane  is  from  the  refracting  surface,  the 
nearer  must  be  the  image-plane.  The  point  to  which  the 
almost  parallel  rays  which  emanate  from  any  very  distant 
point    in    the    axis    converge,    is    called    the    principal 


THE   LENS.  107 

focus.  In  the  unacconiniodatcd  eye  this  point  is  in  the 
retina.* 

The  Lens. — When  the  tensor  of  the  choroid  is  inactive, 
the  principal  focus  of  the  normal  (emmetropic)  eye  lies  in 
the  retina ;  consequently  those  objects  only  are  seen  dis- 
tinctly from  which  the  eye  receives  parallel  rays.  The 
process  by  which  it  is  adjusted  for  vision  of  near  objects, 
is  called  "  accommodation."  Its  accomplishment  is  the 
purpose  or  function  of  the  lens,  and  of  the  muscular  and 
fibrous  structures  by  which  its  form  is  regulated,  the 
tensor  of  the  choroid  and  the  zonule  of  Zinn.  The  tensor 
of  the  choroid  consists,  in  man,  of  fibres  of  two  kinds,  viz., 
of  annular  fibres  which  encircle  the  border  of  the  lens,  and 
of  much  more  numerous  meridional  fibres  which  draw  the 
choroid  towards  the  cornea.  When  (in  the  dog)  this 
muscle  is  thrown  into  action  by  excitation  of  the  short 
root  of  the  lenticular  ganglion,  the  anterior  surface  of  the 
lens  becomes  more  convex  and  approaches  to  a  shorter 
distance  from  the  posterior  surface  of  the  cornea. 

The  increase  of  convexity  is  due  to  the  relaxation  of 
the  zonule,  by  virtue  of  which  the  lens  is  left  to  its  own 
elasticity,  and  assumes  a  form  approaching  that  which  it 
possesses  after  removal  from  the  body.  Under  the  influence 
of  atropin  the  tensor  is  completely  paralysed  ;  in  conse- 
quence, the  convexity  of  the  lens  is  diminished  ;  for,  in  the 
ordinary  condition  of  the  eye,  the  muscular  fibres  are  not 
entirely  relaxed.  The  degree  of  accommodation  of  which 
the  eye  is  capable  varies  in  different  individuals  at  different 
ages.  Thus,  in  the  normal  emmetropic  eye,  which,  when 
entirely  relaxed,  sees  distant  objects  distinctly,  the  lens  can 
in  childhood  be  rendered  convex  enough  to  give  well-defined 
images  of  objects  at  a  distance  of  3  inches.  As  age  advances, 

*  The  statement  above  is  simplified  to  the  utmost  by  the  substitution  of  the 
hypothetical  lensless  eye  for  the  schematic  eye.  All  that  has  been  said  is 
applicable  to  the  real  eye,  but  much  is  omitted.  Those  who  desire  to  under- 
stand in  what  way  the  formation  of  the  image  is  modified  by  the  presence  of 
the  lens,  will  find  it  clearly  explained  in  Hermann's  Physiologj',  pp.  377-384- 


I08  ACCOMMODATION. 

this  distance  (the  "  near  limit "  of  vision)  at  first  slowly,  then 
more  rapidly  lengthens,  until  at  50,  nothing  nearer  than 
12  inches  ;  at  60,  nothing  nearer  then  24  inches  can  be 
defined.  Whence  it  results  that,  inasmuch  as  the  form  of 
the  lens  when  unaccommodated  remains  nearly  the  same, 
the  range  of  adjustment  in  advanced  life  is  exceedingly 
small.  The  term  myopia  is  applied  to  the  condition  in 
which  the  lens  is  too  convex  for  parallel  rays,  even  when 
the  eye  is  atropinized  ;  hypermetropia,  to  that  in  which  it 
does  not  become  convex  enough  for  parallel  rays,  even 
when  the  tensor  is  in  full  action.  In  the  former  case  the 
defect  must  be  compensated  by  concave,  in  the  latter  by 
convex  lenses. 

The  methods  used  for  measuring  the  limit  of  near  vision, 
are  founded  on  an  experiment  known  as  Scheiner's,  A 
diaphragm  having  two  minute  apertures  at  a  distance 
less  than  that  of  the  width  of  the  pupil,  is  placed  immedi- 
ately in  front  of  the  cornea,  while  the  eye  is  kept  fixed  on 
an  object-point,  at  a  sufficient  distance  to  be  distinctly 
defined.  If  now  the  object  is  gradually  brought  nearer,  it 
is  observed,  that  as  soon  as  the  "  near  limit  "  is  passed,  it  is 
seen  double.  The  instrument  used  for  making  this  experi- 
ment with  exactitude  is  called  an  optometer. 

For  all  investigations  relating  to  accommodation,  it  is  of 
importance  to  be  able  to  determine  in  the  living  eye  the 
convexity  of  the  anterior  surface  of  the  lens,  under  different 
conditions.  This  is  done  by  measuring  the  apparent 
diameter  of  an  object  seen  reflected  in  it.  The  instrument 
used  is  called  an  ophthalmometer. 

When  the  eye  is  contemplated  by  an  observer  so  placed  that  the  direction  in 
which  he  looks  at  it  makes  an  angle  of  about  20"  with  the  axis  of  the  observed 
eye,  the  image  of  any  luminous  object  also  placed  in  front  of  the  eye,  rays 
from  which  form  the  same  angle  with  the  axis  but  on  the  opposite  side,  is  seen 
reflected  in  the  middle  of  the  cornea,  and  therefore,  apparently,  close  to  the 
far  border  of  the  pupil.  On  the  near  side  of  this  image  a  second  appears 
similar  to  it,  but  larger,  feebler,  and  indistinct.  When  the  observed  eye  is 
accommodated,  this  image  becomes  smaller  and  a  little  more  sharply  defined. 


THE    RETINA.  ICX) 

Astii^ttatism. — This  term  is  applied  to  a  condition  of  the  eyes  in  which  the 
curvature  of  the  cornea  is  somewhat  less  in  the  vertical  than  in  the  horizontal 
meridian.  If  such  an  eye  is  so  accommodated  that  rays  which  lie  in  the 
vertical  meridian  converge  to  the  retina,  while  those  in  the  horizontal  meridian 
converge  beyond  it,  the  point  is  seen  as  a  horizontal  bar. 

CInotnalism. — If  the  eye  is  fixed  on  a  luminous  point  at  a  great  distance,  it 
often  appears  as  if  it  had  a  sharply  defined  red  centre,  surrounded  by  a  luminous 
fringe.  This  happens  when  the  accommodation  is  such  that  the  less  refrangible 
rays  converge  to  the  retina,  the  more  refrangible  in  front  of  it.  In  the  contrary 
case,  i.e.  when  the  distance  of  the  luminous  point  is  less  than  that  for  which 
the  eye  is  accommodated,  the  centre  is  blue. 

Entointnatic  z'ision. — Shadows  of  objects  floating  in  the  media  of  the  eye 
are  distinguished  by  the  retina,  when  the  eye  is  illuminated  from  a  point  which 
is  so  near  the  cornea  that  the  rays  in  entering  the  eye  become  parallel.  As 
thus  seen,  objects  behind  the  pupil  may  be  distinguished  from  objects  in  front 
of  it,  by  the  observation  that  they  appear  to  mcve  in  the  direction  opposite  to 
that  in  which  the  source  of  light  is  moved. 

Reflection  of  light  in  the  Eyeball. — Light  which  reaches 
the  retina  is  partly  absorbed,  partly  reflected.  Every  re- 
flected ray  returns  approximately  in  the  path  of  its  incidence. 
Consequently,  although  the  cavity  of  the  globe  appears 
under  ordinary  circumstances  dark,  it  can  be  made  to 
appear  luminous  if  illuminated  by  light  which  reaches  it  as 
if  it  came  from  the  eye  of  the  observer.  Thus,  if  a  plate 
of  glass  be  so  placed  between  the  observing  and  the 
observed  eye  that  light  emanating  from  a  luminous  source 
is  reflected  by  it  into  the  observed  eye,  as  if  it  came  from 
the  other,  the  former  appears  bright ;  and  if  it  were  possible 
for  both  eyes  to  remain  relaxed,  that  is  accommodated  for 
extreme  distance,  a  distinct  image  of  the  retina  would  be 
seen  by  the  observing  eye.  In  the  ophthalmoscope  as 
originally  invented  by  Helmholtz,  this  is  done  by  the 
interposition  of  a  concave  correcting  lens  between  the 
observing  eye  and  the  mirror. 

The  Retina. — The  retina  is  a  sensory  end-organ  excited 
by  light.  Its  excitability  has  its  exclusive  seat  in  the 
bacillary  layer. 

If  a  strong  light  is  suddenly  thrown,  by  a  lens,  on  the  outside  of  the  eyeball 
of  a  person  in  a  dark  room,  an  appearance  of  branching  blood-vessels  is  seen 
by  him,  of  which  the  explanation  is  that  the  side  light  throws  shadows  of  the 


no  THE   RETINA. 

retinal  vessels  on  parts  of  the  bacillary  membrane,  which  are  not  accustomed 
to  receive  them.  If  the  source  of  light  moves,  the  shadows  move  with  it, 
and  in  the  same  apparent  direction.  The  motion  of  the  retinal  image  (i)  can 
be  measured  ;  that  of  the  light  (2)  can  also  be  measured,  and  the  distance  (3) 
of  the  vessels  from  the  bacillary  membrane  is  known.  If  from  2  and  3,  i  be 
calculated,  it  will  be  found  to  agi-ee  with  the  measurement. 

The  fovea  centralis  is  more  perfect  structurally  and  func- 
tionally than  any  other  part  of  the  retina.  Accordingly,  as  it 
lies  approximately  in  the  axis  of  the  eyeball,  objects  which 
lie  in  the  prolongation  of  this  axis  (the  visual  line)  i.e.  those 
on  which  the  eye  is  fixed,  are  seen  more  distinctly  than  any 
others.  Thus,  two  objects  so  near  together  that  the  straight 
lines  leading  from  them  to  the  crossing  point  of  the  eye, 
meet  each  other  at  an  angle  of  60"  or  70"  (and  of  which  con- 
sequently the  retinal  images  are  at  most  0*005  millimeter 
from  each  other),  can  be  distinguished  as  two.  If  the 
images  fall  on  the  retina  outside  of  the  fovea,  they  must 
be  at  least  a  millimeter  apart,  in  order  to  be  distinguished. 
If  the  rays  from  two  objects  at  the  same  apparent  height 
meet  at  15^  and  the  eye  is  fixed  on  the  one  nearest  the 
middle  plane  of  the  body,  the  other  (provided  that  its 
retinal  image  does  not  measure  more  than  1-5  millimeter) 
is  not  seen,  for  its  image  falls  on  the  entrance  of  the  optic 
nerve,  the  so  called  "  blind  spot." 

Retinal  Purple. — The  external  layer  of  the  bacillary  membrane  (outer  joints 
of  the  rods  and  cones)  is  infiltrated  with  a  red  colouring  matter,  which  in  the 
eye  removed  from  the  body,  remains  unaltered  so  long  as  the  retina  is  in  the 
dark,  or  is  exposed  only  to  yellow  light.  On  exposure  to  ordinary  or  blue 
light  it  disappears,  but  can  be  restored  even  after  the  cessation  of  the  circula- 
tion, by  contact  in  the  dark  with  the  pigment  epithelium.  During  life  it  is 
alternately  destroyed  and  reproduced  according  as  the  eye  is  exposed,  or  not 
to  light. 

Excitability  of  the  retina. — Process  of  excitation  in  the 
retina.  As  with  respect  to  other  excitable  structures,  so  in 
the  case  of  the  retina,  we  may  best  distinguish  between  the 
excitation  and  the  physiological  effect  which  it  occasions 
(sensation  of  light),  by  studying  their  time-relations.  We 
learn  by  observation,  (i)  that  the  sensation  of  light  produced 


SENSATIONS   OF  COLOUR.  I  1 1 

by  an  instantaneous  excitation  (say  of -pjg")  at  first  increases, 
culminates  about  ^"  after  the  excitation  and  then  rapidly 
diminishes ;  (2)  that  of  a  succession  of  such  excitations 
following  each  other  without  intermission,  all  are  at  first 
(during  the  first  tenth  of  a  second)  equally  effective,  so 
that  the  sensation  occasioned  by  the  series  is  equal  to  the 
sum  of  the  sensations  which  would  have  been  produced  by 
all  of  the  excitations  had  they  occurred  separately ;  but 
aftenvards  the  excitations  become  less  and  less  effective. 
Hence  it  results,  first,  that  in  the  case  of  illuminations  of 
the  unexhausted  retina  of  about  ^y  duration  or  less,  the 
sensation  of  light  is  proportional  to  the  product  of  the 
intensity  and  duration  of  the  illumination  ;  and  secondly, 
that  when  the  illumination  is  continued,  the  sensation  of 
light  at  first  increases,  then  gradually  diminishes.  This 
diminution  of  the  excitability  of  the  retina  by  previous 
excitation  is  called  "  exhaustion."  In  consequence  of  it, 
when  we  contemplate  a  bright  object  and  then  look  else- 
where, we  see  a  dark  image  (called  an  after-image)  of  it. 

When  the  retina  is  excited  by  homogeneous  rays,  /'.  e., 
by  rays  of  which  all  are  of  the  same  refrangibility,  the 
effects  follow  each  other  in  the  same  order,  but  it  is 
found  that  the  colour-sensations  occasioned  by  rays  of 
equal  intensity,  but  different  refrangibility,  culminate  at 
different  rates.  The  exhaustion  produced  by  monochro- 
matic light  affects  the  excitability  of  the  retina  only  in 
respect  of  light  of  the  same  kind.  Consequently,  the 
after-images  of  coloured  objects  are  themselves  coloured. 
Colour  sensations  are  said  to  be  "  blended  "  when  the 
rays  which  occasion  them  affect  the  retina,  either  simul- 
taneously or  in  such  rapid  succession  that  their  action  is 
simultaneous.  If  two  kinds  of  light  act  simultaneously 
on  both  retinae,  they  may  also  give  rise  to  a  blended 
sensation. 

Classification  of  colour-sensations : — The  sensations  oc- 
casioned by  monochromatic  rays  of  different  kinds  admit 


112  SENSATIONS   OF   COLOUR. 

of  being  placed  in  linear  series,  in  the  order  of  the  refran- 
gibility  of  the  rays  which  produce  them.  Those  occasioned 
by  the  simultaneous  action  of  rays  of  different  refrangi- 
bilities  are  much  more  various,  and  cannot  be  arranged  in 
line.  If,  however,  on  a  plane  surface  a  central  position  is 
assigned  to  the  sensation  "  white,"  the  other  sensations  may 
be  arranged  round  it  in  such  a  way,  that  the  sensation 
which  results  from  the  "blending"  of  any  two  or  more 
others  has  its  place  between  them,  at  distances  from  each 
which  express  their  relative  preponderances.  In  this 
arrangement  (called  the  colour  circle)  spectral  colour  sensa- 
tions form  an  incomplete  ring  round  white,  between  the  red 
and  violet  ends  of  which  is  placed  purple.  The  relations 
of  colour  sensations  exhibited  in  the  colour  circle  can  be 
most  simply  explained  on  the  following  hypothesis.  (Young, 
Helmholtz.)  There  are  three  fundamental  colour-sensations, 
viz.  :  red,  green  and  indigo,  from  which  all  others  are  derived 
by  blending.  Every  element  of  the  retina  (every  cone) 
contains  three  terminal  elements,  one  of  which  is  most 
excited  by  the  less  refrangible  rays  (red  element),  one  by 
the  most  refrangible  (blue  element),  the  other  by  those  of 
medium  refrangibility  (green  element),  but  all  more  or  less 
by  all. 

The  theory  that  red,  green,  and  indigo,  are  the  fundamental  sensations  is 
supported  by  the  following  observations,  among  others: — i.  If  the  spectrum 
is  contemplated  while  its  colours  are  gradually  weakened,  until  they  cease  to 
be  visible,  the  colours  named  are  the  last  to  disappear.  (Briicke.)  2.  If  a 
white  surface  is  contemplated  by  a  retina  of  which  the  excitability  for  a  par- 
ticular kind  of  homogeneous  light  has  been  weakened  by  excitation,  it  appears 
to  be  coloured  ;  the  colour  sensation  produced  occupies  a  place  in  the  colour 
circle  exactly  opposite  to  that  immediately  occasioned  by  the  excitation,  and  is 
therefore  said  to  be  "complementary"  to  it.  In  like  manner,  if  a  coloured 
surface  is  contemplated  by  a  retina  partially  dulled  by  the  same  mode  of 
excitation,  its  hue  is — provided  that  its  colour  is  a  blended  one — altered,  by  the 
weakening  of  one  of  its  constituent  sensations.  But  if  after  dulling  the  excit- 
ability of  the  retina  for  red,  an  indigo  surface  is  contemplated,  its  hue 
remains  unchanged,  for  inasmuch  as,  according  to  the  theory,  indigo  rays 
scarcely  affect  the  red  elements,  the  quality  of  the  sensation  is  not  affected  by 
their  not  taking  part  in  its  production  ;  if  the   experiment  is  repeated  with  a 


MOTIONS   OF   THE   EYEBALLS.  113 

violet  surface,  the  result  is  no  longer  the  same.  To  the  retina  dulled  for  red  it 
appears  bluer.  Similar  observations  may  be  made  as  regards  the  other 
primary  colours.  3.  The  image  seen  in  the  dark  after  the  eye  has  been 
directed  to  the  sun  is  at  first  bright,  then  fades  away  and  becomes  red.  If 
•while  the  red  image  is  observed  white  light  is  admitted,  it  becomes  green. 
The  excitation  of  the  red  elements  is  more  persistent  than  of  the  others,  and 
their  consequent  exhaustion  more  prolonged. 

Colour-blindness. — In  some  persons  (in  consequence,  it 
may  be  supposed,  of  defective  excitability  of  the  green  or 
red  elements  of  the  cones),  red,  in  others  green  is  mistaken 
for  grey.  About  two  in  every  hundred  railway  officials 
examined  by  Bonders,  were  found  to  present  one  or  other 
of  these  conditions. 

Motions  {Rotations)  of  the  Eyeballs. — i.  The  straight  line 
which  connects  the  apex  of  the  cornea  with  the  fovea 
centralis  retinae  is  called  the  "  visual  axis."  The  plane  in 
which  the  visual  axes  of  both  eyes  lie  is  the  "  visual  plane." 
When  the  visual  axes  of  both  eyes  are  directed  to  the 
horizon  and  are  parallel  to  the  middle  plane  of  the  body, 
the  eyes  are  in  the  "  position  of  rest  "  (primary  position). 
2.  The  vertical  plane  in  which  the  visual  axis  lies  when  the 
eyes  are  in  the  position  of  rest,  is  called  the  "  vertical 
meridian  "  and  the  horizontal  plane  at  right  angles  to  it, 
the  "horizontal  meridian"  3.  All  rotations  of  the  eye- 
balls take  place  round  axes  (called  "  axes  of  rotation ") 
which  cut  the  visual  axis  at  right  angles,  about  17  millim. 
behind  its  mid-point.  (Listing  and  Bonders.)  4.  Any 
position  into  which  the  eyeballs  can  be  brought  by  rotat- 
ing them  from  the  position  of  rest  directly  upwards  {i.e., 
round  horizontal  and  coincident  axes  of  rotation),  or  directly 
to  the  right  or  left  {i.e.,  round  vertical  axes  of  rotation),  is 
called  a  secondary  position.  5.  In  the  position  of  rest 
and  in  every  secondary  position,  the  horizontal  meridians  of 
both  eyes  are  in  the  visual  plane.  All  other  positions  are 
called  "  tertiary."  In  every  tertiary  position,  the  horizontal 
meridians  intersect  the  visual  plane,  at  an  angle  which  is 
called  the  "angle  of  rotation."     (See  Exercises.) 

I 


114  MOTIONS  OF  THE  EYEBALLS. 

The  muscles  of  the  eyeball  are  divisible  in  respect  of 
their  action,  into  two  groups,  of  which  one  comprises 
the  rectus  interniis  and  r.  extenms ;  the  other,  the 
ohliqiins  inferior,  and  o.  stiperior,  which  act  in  concert  with 
the  rectus  s2cperior  and  r.  inferior.  The  axis  round  which 
any  muscle  rotates  the  eyeball  is  called  its  proper  axis  of 
rotation.  Those  of  the  internal  and  external  recti  nearly 
coincide  with  the  vertical  axis  of  the  eyeball.  Consequently 
these  muscles,  acting  antagonistically,  rotate  the  eyes 
directly  to  right  or  left  (secondary  positions).  The  com- 
bined axis  of  the  oblique  muscles  (the  axes  of  the  two 
being  approximately  identical)  is  horizontal,  but  cuts  the 
equator  of  the  eye  at  an  angle  of  60°.  The  combined  axis 
of  the  superior  and  inferior  recti  is  neither  horizontal  nor 
transverse,  but  has  its  inner  end  lower,  as  well  as  further 
forwards  than  the  outer.  If,  however,  the  rectus  sup. 
acts  with  the  obliquus  inf ,  they  together  rotate  the  eye 
round  an  axis  which  lies  between  their  own  axes,  and 
nearly  coincides  with  the  horizontal  axis  of  the  eyeball : 
the  obliquus  superior  acts  similarly  in  conjunction  with  the 
rectus  inferior.  Thus  rotations  of  the  eyeball  from  the 
rest  position  into  secondary  positions  are  performed,  if  to 
right  or  left,  by  the  internal  and  external  recti,  if  upwards 
and  downwards,  by  the  combined  action  of  the  other  four 
muscles. 

When  the  eyes  are  so  fixed  on  any  point  that  it  lies  in 
the  visual  axis  of  both  of  them,  the  point  so  contemplated 
is  seen  singly  and  perfectly  ;  and  all  other  points  are  seen 
singly,  but  not  perfectly,  which  are  received  by  corre- 
sponding points  of  the  two  retinje — that  is  by  points  which 
would  exactly  cover  each  other  if  it  were  possible  for  both 
eyes  to  occupy  the  same  position,  the  vertical  and  horizon- 
tal meridians  respectively  coinciding. 

Mental  Interpretations  or  jfndgjnents  of  Visual  Sensa- 
tions.—  I.  Binocular  blending  of  colours.  When  rays  of  two 
colours  enter  the  two  rctinai  simultaneously,  the  sensation 


HEARING.  115 

is  not  always  the  same.  Sometimes  the  two  colours  arc 
blended  as  completely  as  if  both  affected  one  retina  :  at 
others  there  is  a  contest  between  the  two,  first  one,  then 
the  other  predominating  in  the  blending.  2.  Judgment  of 
distance.  We  judge  of  the  distance  of  any  object,  chiefly 
by  the  degree  of  convergence  of  the  visual  axes,  which  wc 
find  necessary  in  order  to  fix  both  eyes  upon  it.  Conse- 
quently, if  one  eye  is  shut  and  two  or  more  objects  of  the 
same  form  but  of  different  sizes  arc  placed  before  the  other 
at  such  distances  that  their  retinal  images  cover  equal 
areas,  their  respective  distances  cannot  be  distinguished. 
If  both  eyes  are  used  a  correct  judgment  can  be  formed 
without  difficulty.  3.  Judgment  of  solidity.  By  explor- 
ing an  object  with  the  eyes,  i.e.,  by  fixing  them  successively 
on  different  points  of  its  visible  surface,  we  are  able  to 
judge  of  the  relative  distances  of  these  points,  as  well  as 
of  their  directions.  It  can,  however,  be  shown  that  this 
process  is  not  ordinarily  employed  in  judging  of  the  form 
and  solidity  of  objects,  but  that  the  mind  accomplishes  this 
instantaneously,  by  the  blending  of  the  two  dissimilar 
images  which  arc  received  by  the  two  retin?e,  whenever 
both  eyes  are  fixed  on  some  point  in  a  solid  object  at  a 
short  distance  from  them.  The  point  so  contemplated  is 
of  course  seen  single,  others  are  for  the  most  part  seen 
double  :  notwithstanding  this,  we  are  not  conscious  of  any 
confusion  of  images. 


Hearing. 

The  process  of  hearing  consists  (i)  in  the  production  of 
vibratory  movements  of  the  membrana  tympani,  which  are 
synchronous  with  the  sound-vibrations  of  air  in  the 
meatus  ;  (2)  in  the  communication  of  these  vibrations  to 
the  liquid  contained  in  the  labyrinth  ;  and  (3)  in  the  pro- 
duction of  vibrations  in  all   those   parts  of   the  lamina 

I  2 


Il6  HEARING. 

spiralis  of  which  the  vibration-rate  agrees  with  those  of 
vibrations  existing  in  the  liquid. 

Sensations  of  sound  are  divided,  according  to  the  cha- 
racter (form)  of  the  air-vibrations  which  occasion  them, 
into  non-musical  sounds  or  noises,  and  musical  sounds 
or  "  tones."  Of  tones,  simple  and  compound  are  distin- 
guished. The  former  are  heard  when  the  air  molecules 
at  the  external  surface  of  the  membrana  tympani  are  in 
simple  pendular  vibration  ;  the  latter  when  the  vibrations 
are  compounded  of  vibrations  of  different  rates  of  fre- 
quency, of  which  the  relations  to  each  other  may  be  1:2, 
1:3,  1:4,  1:5,  and  so  on  in  the  same  order.  The  tones 
which  correspond  to  each  of  these  simple  constituent 
vibrations,  are  called  "  partial  tones."  According  to  the 
number,  relative  strength  and  relative  frequency  of  the 
simple  tones  into  which  they  can  be  resolved,  compound 
tones  differ  in  timbre  or  quality.  Tones  whether  simple 
or  compound  differ  also  in  pitch :  the  pitch  of  a  simple 
tone  is  expressed  by  the  number  of  its  vibrations  in  a 
second  :  that  of  a  compound  tone  by  the  vibration-number 
of  its  predominant  partial-tone. 

The  middle  ear. — The  cavity  of  the  tympanum  across 
which  sonorous  vibrations  are  transmitted  by  the  ear 
bones,  communicates  with  the  pharynx  by  the  Eustachian 
tube :  the  pharyngeal  end  of  this  tube  is,  however,  usually 
closed  and  can  only  be  opened  by  bringing  into  action 
the  muscles  of  deglutition.  The  external  wall  of  the 
cavity  is  formed  by  the  membrana  tympani,  which,  by  the 
arrangement  of  the  radiating  and  annular  fibres  which 
compose  its  two  layers,  by  the  conical  form  of  its  internal 
surface,  and  by  the  mode  of  attachment  of  the  handle  of 
the  malleus,  is  fitted  for  its  function — the  passive  reception  of 
the  motions  communicated  to  it  by  the  vibrating  air  parti- 
cles at  its  surface.  In  the  communication  of  the  move- 
ments of  the  membrana  tympani  to  the  foramen  ovale,  the 
malleus  and  incus  act  as  one  piece  ;  for,  so  long  as  the  mem- 


HEARING.  117 

brana  tympani  is  tense,  the  tooth  of  the  incus  is  kept  locked 
against  the  notch  of  the  malleus.  When  in  this  con- 
dition, the  two  bones  rotate  on  an  axis  of  which  one 
extremity  is  at  the  tip  of  the  short  process  of  the  incus, 
the  other  corresponding  approximately  to  the  attachment 
of  the  ligamentum  anterius  of  the  malleus :  hence  the 
axis  of  rotation  nearly  coincides  with  the  upper  border 
of  the  tympanic  ring.  The  two  bones  may  be  compared 
when  in  action  to  a  bell-crank  lever  of  which  one  limb, 
representing  the  handle  of  the  malleus,  is  approximately 
half  as  long  again  as  the  other  (the  long  process  of  the 
incus),  and  forms  with  it  an  acute  angle.  Consequently 
every  motion  of  the  tympanic  membrane  which  is  trans- 
mitted to  the  stapes  is  diminished  by  about  a  third. 
When  the  membrana  tympani  is  relaxed,  the  distance 
between  the  tip  of  the  long  process  of  the  incus  and  the 
handle  of  the  malleus  slightly  increases.  Nothing  can  be 
certainly  stated  as  to  the  uses  of  the  muscles  of  the 
middle  ear. 

The  internal  car. — The  essential  part  of  the  organ  of 
hearing  is  the  cochlea  and  particularly  the  organ  of  Corti. 
The  organ  of  Corti  consists  of  a  series  of  arches,  about 
3,000  in  number,  of  extreme  minuteness,  the  span  of  which 
increases  gradually  from  the  base  of  the  cochlea  to  the 
helicotrema,  and  of  epithelial  elements  (the  hair-cells)  in 
relation  with  these  arches,  which  are  intimately  connected 
with  the  terminations  of  the  cochlear  nerve.  These  struc- 
tures rest  upon  a  ribbon-shaped  fibrous  membrane  (the 
lamina  spiralis  membranacea  or  membrana  basilaris) 
which  is  wide  at  the  helicotrema,  narrow  at  the  base  of 
the  cochlea.  It  is  attached  by  its  edges  to  bone,  and  con- 
sists chiefly  of  fibres  which  run  transversely  to  its  length, 
and  are  believed  to  be  tense.  Corti's  organ  is  contained 
in  a  spiral  tube,  triangular  in  section,  the  duct  of  the 
cochlea,  one  side  of  which  is  formed  by  the  membrana 
basilaris,  the  other  by  the  membrane  of  Reissner. 


Il8  HEARING. 

With  reference  to  the  transmission  of  sound,  the  cavity 
of  the  vestibule  and  cochlea  may  be  regarded  as  divided 
into  two,  that  of  the  vestibule  and  scala  vestibuli 
which  communicates  with  the  lymph  space  surrounding 
the  vestibular  sacs,  and  that  of  the  scala  tympani,  which 
is  closed  by  the  membrane  of  the  fenestra  ovalis. 
Although  these  two  cavities  communicate  by  a  small 
opening,  they  may  be  regarded  as  in  so  far  separate  that 
any  motion  of  the  membrane  of  the  foramen  ovale  must 
be  communicated  to  the  membrane  of  Reissner,  then  to 
the  membrana  basilaris  and  thereby  to  the  organ  of  Corti. 
From  the  structure  of  the  organ  of  Corti  it  was  inferred 
by  Helmholtz  that  it  must  be  an  organ  for  the  perception 
and  discrimination  of  tones,  and  that  the  elements  (nerve- 
endings,  Corti's  arches  and  adjoining  cells)  serve  in  the 
discrimination  of  the  sonorous  vibrations  of  the  liquid  in 
which  they  are  immersed — a  function  which  is  analogous 
to  that  of  the  hypothetical  red,  blue,  and  green  elements 
of  the  retinal  cones  in  regard  to  luminous  vibrations. 
Tones  can  be  readily  discriminated  by  the  human  ear  of 
which  the  vibration-rates  range  from  40  to  7,000  per  second. 
A  skilled  musical  ear  can  distinguish  more  than  6,000 
different  tones  within  the  range  of  these  seven  and  a  half 
octaves  ;  consequently,  as  there  are  only  3,000  arches  of 
Corti,  each  must  be  capable  of  being  excited  by  several 
gradations  of  tone. 

In  the  case  of  the  elements  of  the  cones  of  the  retina 
we  can  form  no  conception  of  the  modes  in  which  they 
are  acted  upon  by  light,  but  the  action  of  tones  on  the 
organ  of  Corti  can  be  satisfactorily  explained  by  com- 
paring that  organ  to  a  system  of  resonators.  By  a  reso- 
nator is  meant  anything  which,  by  virtue  of  its  form  and 
structure,  is  capable  of  being  thrown  into  musical  vibra- 
tion. Every  resonator  produces  when  thus  acted  upon,  a 
tone  which  is  peculiar  to  itself — its  "  proper  tone,"  and  is 
readily  excited  by  tones  of  the  same  vibration- rate  when 


TASTE.  1  19 

communicated  to  it  cither  through  the  air  or  otherwise. 
Many  resonators  can  be  excited  to  vibration  not  only  by 
their  "  proper  tones,"  but  also  by  vibrations  of  approxi- 
mately tile  same  frequency,  in  a  degree  proportional  to 
the  approximation.  As  there  is  reason  to  believe  that  the 
resonators  of  the  organ  of  Corti  have  this  property,  it 
enables  us  to  understand  how  it  happens  that  the  number 
of  distinguishable  tones  exceeds  that  of  the  elements 
which  serve  to  appreciate  them.  For  a  tone  affects  not 
one,  but  two  or  more  resonators,  each  in  proportion  to  its 
proximity  to  the  tone  by  which  it  is  excited,  so  that  just 
as  every  perception  of  colour  is  founded  on  impressions 
received  through  at  least  three  elements,  every  perception 
of  tone  is  occasioned  by  the  simultaneous  vibration  of 
several  elements  of  the  organ  of  Corti.  The  power  of 
distinguishing  two  tones  which  follow  each  other  at  very 
short  intervals  of  time,  is  known  to  vary  with  their  rate 
of  vibration.  '"'^Thus,  whatever  be  the  tone,  it  has  been 
found  that  the  time  intervening  between  one  excitation 
and  its  successor  must  be  sufficient  for  about  twenty-two 
vibrations  in  order  that  they  may  be  heard  as  two.  Helm- 
holtz  explains  this  on  the  principle  that  the  resonators  of 
the  organ  of  Corti  are  very  readily  thrown  into  vibration, 
and  continue  to  vibrate  only  a  short  time  after  the  excita- 
tion has  ceased. 

Nothing  can  be  stated  with  certainty  as  to  the  functions 
of  the  end-organs  of  the  vestibular  sacs  ;  from  their 
analogy  with  the  auditory  vesicles  of  invertebrate  animals 
without  cochlear  it  may  be  inferred  that  they  have  similar 
functions.     (With  reference  to  the  ampullae,  see  p.  97). 

Taste. 

Sensations  of  taste  are  occasioned  by  the  access  of 
sapid  substances  to  the  tongue,  either  in  the  neighbour- 
hood of  the  papillae  vallatae,  or  of  the  papilla  foliata  of 


I20  TASTE. 

either  side,  or  to  its  upper  surface  close  to  the  tip.  Ahnost 
all  unmixed  sensations  of  taste  may  be  referred  to  one  of 
four  fundamental  kinds,  viz.,  bitter,  sweet,  salty,  and  acid. 
Those  which  cannot  be  so  classified  result  for  the  most 
part  from  the  "  blending "  of  gustatory  with  tactile  or 
olfactory  impressions.  Of  the  four  fundamental  tastes, 
all  can  be  appreciated  by  the  papillae  vallatse  and  the 
papillae  foliatae.  The  tasting  power  of  the  tip  is  im- 
perfect, and  in  some  persons  wanting.  When  present, 
it  is  in  most  persons  confined  to  the  appreciation  of  acid, 
sweet  and  salty  tastes.  Taste  sensations  can  be  excited 
by  the  passage  of  voltaic  currents  through  the  base  of 
the  tongue,  particularly  when  the  anode  is  applied  to 
the  neighbourhood  of  the  papillae  vallatae,  or  to  the 
papilla  foliata  of  either  side.  Taste  is  believed  to  be 
dependent  on  the  excitation  of  certain  end-organs,  the 
so-called  taste  buds,  which  are  to  be  found  in  the  struc- 
tures above  mentioned.  As,  after  section  of  the  glosso- 
pharyngeal nerve  in  animals,  these  organs  degenerate  and 
finally  disappear,  there  can  be  little  doubt  that  they  con- 
tain the  gustatory  terminations  of  that  nerve.  In  judging 
of  their  function  it  must  remembered  that  they  are  met 
with  beyond  the  limits  of  the  gustatory  region,  as,  e.g.^ 
on  the  under  surface  of  the  epiglottis,  in  the  larynx  and 
in  the  papillae  fungiformes  of  parts  of  the  tongue  which 
are  not  endowed  with  taste. 

The  taste  region  at  the  base  of  the  tongue  is  supplied 
by  the  glossopharyngeal  nerve.  The  tip  of  the  tongue 
receives  its  supplies  from  the  lingual,  and  has  been  found 
in  several  instances  in  man  to  lose  its  tasting  power  after 
destruction  of  that  nerve.  There  is,  however,  reason  for 
believing  that  the  gustatory  fibres  of  the  lingual  are  ulti- 
mately derived  from  the  glossopharyngeal  nerve,  through 
the  tympanic  plexus.  In  animals,  after  section  of  the 
glossopharyngeal  nerves,  near  their  origin,  taste  appears, 
to  be  entirely  absent. 


SMELL.  121 


Smell. 


Sensations  of  smell  are  occasioned  when  air  containing 
odorous  substances  in  the  state  of  vapour  or  gas  is  inspired 
through  the  nostrils,  but  not  when  the  cavity  of  the  nares 
is  filled  with  their  solution. 

Smell  is  limited  to  the  upper  part  of  the  septum,  the 
upper  turbinated  bone,  and  the  upper  part  of  the  middle 
turbinated  bone.  This  region  is  characterized  by  its 
yellow  colour,  by  its  slender  columnar  epithelial  ele- 
ments, and  by  the  existence  among  them  of  the  peculiar 
spindle-shaped  elements,  which  are  believed  to  be  the  end- 
organs  of  the  nerve  of  smell.  In  inspiration,  a  large  pro- 
portion of  the  air  inspired  passes  through  the  olfactory 
region ;  but,  in  consequence  of  the  form  of  the  channel 
through  whictflt  passes,  the  expiratory  current  is  almost 
entirely  diverted,  so  that  odours  of  intrinsic  origin  are  but 
little  perceived.  The  varieties  of  smell  are  more  numerous 
than  those  of  taste,  and  appear  to  have  little  relation  to 
the  chemical  constitution  of  the  gases  or  vapours  which 
occasion  them. 


123 


PRACTICAL    EXERCISES] 

RELATING  TO  THE   PHYSIOLOGICAL   PROPERTIES  OF  THE 

CONTRACTILE     AND     EXCITABLE 
TISSUES. 


I. — Modes  of  Excitation. 


[Electrical  Excitation. — The  requirements  for  the  purpose  are 
Batteries  (Grove's  or  Daniell's),  an  Induction  coil,  wires,  two  keys,  and  suit- 
able Electrodes.  The  Induction  apparatus  used  is  that  of  Prof,  du  Bois-Rey- 
mond.  (See  "  Handbook,"  p.  351,  fig.  298.)  The  key  ordinarily  used  is  also 
that  of  du  Bois-Reymond.  The  Electrodes  are  made  as  follows  : — Cement 
with  sealing-w-ax  two  copper  wires,  each  about  three  inches  long  and  pointed 
at  one  end,  into  two  pieces  of  glass  tube  two  inches  long,  just  large  enough  to 
contain  the  wires.  The  ends  of  the  wires  must  project  about  half  an  inch 
from  the  glass  tubes,  and  must  be  coated  on  all  sides,  excepting  one,  with 
sealing-wax.  Bind  the  two  glass  tubes  together  with  strong  thread  and 
solder  fine  copper  wires  to  the  blunt  ends  of  the  electrodes. 

I.  Use  of  the  Induction  Coil. — «•  For  single  induction  shocks. — 
Connect  a  Daniell  cell  by  copper  wires  with  the  two  upper  screws  which  are 
directly  connected  with  the  ends  of  the  primary  coil,  interposing  a  key  in  the 
circuit.  Insert  the  wires  from  the  electrodes  in  the  binding  screws  of  the 
secondary  coil,  and  place  the  points  of  the  electrodes  against  the  tongue. 
Withdraw  the  secondary  coil  from  the  primaiy  and  then  gradually  bring  it 
nearer,  opening  and  closing  the  key  after  each  approximation.  The  "break 
shock"  is  first  felt,  and  is  throughout  perceptibly  stronger  than  the  "make 
shock."  b.  For  faradization. — Connect  the  battery  wires  with  the  screws  at 
the  bases  of  the  brass  pillars  (C  and  A  in  fig.  293).  If  the  platinum-pointed 
screw  (/)  is  properly  adjusted,  the  hammer  begins  to  vibrate  on  closing  the 
key,  and  a  series,  consisting  alternately  of  "make"  and  "break"  shocks,  is  felt, 
which,  as  the  secondary  coil  begins  to  cover  the  primary,  becomes  unbearable. 
For  many  purposes  it  is  desirable  to  avoid  the  great  disparity  which  in  the 
ordinary  arrangement  exists  between  the  opening  and  closing  shocks.  This  is 
accomplished  by  a  contrivance  known  as  Helmholtz'  modification  {see  "  Hand- 
book," fig.  294)  : — A  side  wire  connects  the  outer  pillar  with  the  top  screw  of 


124  ELECTRICAL  EXCITATION. 

the  sar:e  s:£e.  Tie  ur^er  rlatizum-rlpped  screw  is  ■withdrawn  and  the  tmder 
f  li±i.in  ::r  br:.-a~':i:  in::  c:z:ac:  wii  the  \-ibrating  hammer,  at  the  moment 
th:::  ::  :;  ir-vm  d:Trr:  bj  the  temporary  magnet.  Compare  the  effects  with 
th:st  ;;  re  •: :  .:;>  felt,  particiilarly  when  the  primary  coil  is  covered  by  the 
secondary.  It  is  conTenient  in  all  cases  to  interpose  a  key  in  the  primary 
circuit. 

2.  Tlie  Single  Induction  Shock. — Connect  the  primary  coil  of  the 
Induction  apparatus  ■ivith  a  Daniell  cell,  interposing  a  key.  Arrange  a  rheo- 
5cop;c  preparation  of  the  lower  limbs  of  a  pithed  frog,  by  placing  two  slender 
glass  rods  under  the  sacral  plexuses,  having  first  opened  the  visceral  cavity  and 
removed  the  viscera.  Connect  the  electrodes  with  the  terminals  of  the 
secondary  coil,  and  place  them  underneath  the  nerves  thus  separated  from 
other  structures.  The  preparation  should  be  supported  in  the  vertical  position 
by  a  damp.  Remove  the  secondary  fix)m  the  primary  coil  until  no  resp>onse 
occuis  cm  closing  or  opening  the  key.  Then  bring  the  secondary  coil  gradually 
nearer  and  ohseTe  that  at  a  certain  distance  the  preparation  responds  only  to 
the  "break"  shock,  afterwards  to  both  "make"  and  "break,"  b»t  more 
strongly  to  the  latter,  zzlz.  nnally  with  equal  vigour  to  both. 

3-  The  Extra  Cnrrent. — To  demonstrate  Faraday's  "  extra  current " 
physiologicaJy,  introitice  the  exciting  electrodes  into  the  primary  circuit  of  the 
induction  apparatus,  removing  the  secondary  coiL  Connect  the  electrodes  bya 
couple  of  copper  wires  whose  ends  are  united  by  a  key,  so  that  when  the  key  is 
closed  the  electrodes  are  in  metallic  connection  by  the  wires  and  key  as  well  as 
by  the  coil  and  battery.  Place  the  electrodes  under  the  sacral  plexus  in  the 
preparation  used  in  the  previous  experiment ;  and  observe  that  when  the  key 
is  opened  the  rheoscopic  limbs  resjxjnd  strongly ;  this  is  due  to  the  extra 
current,  that  is,  to  the  induction  current  which  is  produced  in  the  primary 
coil  in  the  same  direction  with  the  battery  current,  immediately  after  the 
sadden  diminution  produced  by  the  of>ening  of  the  key. 

4-  Unipolar  Excitation. — Connect  one  electrode  with  one  terminal 
of  the  induction  coil  and  place  it  under  the  sacral  ner\-e5  of  the  same  pre- 
paration, which  for  thi";  purpose  must  be  on  a  glass  plate.  No  response  takes 
place  either  on  making  or  breaking.  Touch  the  preparation  or  otherwise 
ccMmect  it  with  the  earth,  and  it  will  be  observed  that  it  responds  at  break. 

5-  Faradization. — Arrange  the  coil  for  faradization  and  place  the 
electrodes  under  the  sacral  plexus  in  a  similar  preparation.  The  limbs  are 
extended  and  the  muscles  rigid.  The  spasm  so  produced  persists,  though 
with  gradually  diminishir^  intensity,  so  long  as  the  primary  circuit  remains 
dosed.     This  condition  of  tonic  contraction  is  designated  Tetanus. 

6.  Galvani's  Experiment.— Take  a  clean  bit  of  zinc  \<ire,  and  coil 
roand  one  end  of  it  a  copper  wire  of  the  same  length,  so  as  to  make  a  fork. 
Pith  a  frog  and  lay  it  on  its  belly.  Remove  the  skin  from  the  back  of  the  thigh, 
separate  with  the  finder  and  remove  the  narrow  ifice/>s  femoris.  Separate  the 
sdatic  nene  which  is  thus  brought  into  new,  from  the  surrounding  struc- 
tures, and  touch  the  nerie  first  with  the  copper  wire,  then  with  the  zinc.  It 
will  be  observed  that  on  closing  the  circuit  thus  formed,  l\it  gastroctumius  muscle 
contracts  and  the  foot  is  extended.  If  it  is  moderately  excitable,  the  same  thing 
happens  also  on  opening  tL 


ELECTRICAL  EXCITATION.  1 25 

7-  Excitation  by  Interruption  of  the  Direct  or  Battery 

Current. — For  this  purpose  it  is  necessar)-  to  arrange  the  circuit  so  that  its 
intensity  can  be  varied  at  will.  This  might  be  accomplished  by  the  inter- 
position of  large  resistances,  but  such  a  method  would  be  so  inconvenient  as 
to  be  impracticable.  The  method  always  used  is  to  connect  the  poles  of  the 
battery  by  a  side  wire,  whose  resistance  can  be  varied  at  pleasure.  As  the 
resistance  of  nerve  and  muscle  is  very  high,  the  strength  of  the  current  in 
the  circuit  varies  approximately  inversely  as  the  resistance  of  the  side  wire. 
A  graduated  side  wire  suitable  for  this  purpose  is  called  a  rheochord.  The 
rheochord  commonly  used  is  that  of  du  Bois-Reymond  ("Handbook," 
fig.  298).  Connect  the  two  terminal  binding  screws  of  the  rheochord  with 
the  battery  (a  single  Daniell's  cell)  interposing  a  key  ;  connect  with  the 
same  binding  screws  the  two  end  screws  of  the  reverser  ("  Handbook," 
figs.  299,  506),  and  finally  insert  the  wires  from  the  electrodes  in  the  two 
central  screws  (i  &  2).  Prepare  the  sacral  plexus  and  rheoscopic  limbs  as 
before,  and  arrange  the  electrodes.  Diminish  the  resistance  of  the  rheochord 
to  the  utmost,  and  observe  that  on  opening  and  closing  the  circuit,  no 
contraction  takes  place.  Then  gradually  increase  the  resistance.  At  first 
the  muscles  respond  only  to  closure,  subsequently  to  "  make"  and  "  break," 
whatever  the  (direction  of  the  current.  On  continuing  the  observation,  par- 
ticularly with  stronger  currents,  it  will  be  observed  that  the  "make"  and 
"  break  "  effects  are  in  no  instance  equal,  and  that  the  nature  of  the  inequality 
is  influenced  by  the  direction  of  the  current.  The  results  are  further  modified 
by  exhaustion  or  injur)-  of  the  ner%-e. 

8.  Excitation  of  a  Motor  Nerve  by  contact  with  a  Con- 
tracting Muscle.    The  Secondary  Twitch— Af-er  preparL-^  the 

sciatic  nerve  as  above  directed,  expose  the  gastrocnemius  as  directed  in  6. 
Seize  its  tendon  with  the  forceps  and  separate  it  from  its  attachments.  Cut  off 
the  tibia  and  femur,  close  to  the  knee  on  either  side,  along  with  the  muscles 
and  other  soft  parts,  taking  care  not  to  injure  the  nerve.  A  gastrocnemius 
with  its  nerve  as  described,  constitute  a  "nerve  muscle  preparation."  Two 
such  preparations  are  required. 

Place  one  of  them,  b,  on  a  glass  plate,  and  fix  the  other,  a,  along  the  tdgs 
of  a  small  piece  of  board.  Then  place  the  board  on  the  glass  plate  in  such  a 
position  that  the  nerve  of  b  can  can  be  readily  laid  on  the  muscle  of  a. 
Excite  by  a  single  induction  shock  passed  through  its  nerve.  At  the  same 
moment  that  a  contracts,  b  will  contract-  Then  repeat  the  experiment,  but 
instead  of  passing  single  induction  shocks,  faradize  the  nerve.  Tetanus  is 
produced  in  b,  which  lasts  so  long  as  a  is  tetanized.  Ascertain  that  the  effect 
is  not  due  to  escape  of  current,  by  ligaturing  the  ner^-e  and  repeating  the 
experiment. 

9-  Mechanical  Excitation.— Mechanical  Tetanus.  Connect  a  Grove 
cell  with  the  "  Tetanometor,"  introducing  a  key  into  the  circuit.  The  wire 
from  the  zinc  terminal  of  the  battery  must  be  inserted  in  the  binding  screw 
marked  Z,  that  from  the  platinum  in  K.  Adjust  the  apparatus  so  that  mi 
closing  the  key  the  ivory  hammer  vibrates  so  as  to  excite,  v*ithout  destroying, 
a  nerve  places;!  on  the  ivory  groove.  The  effect  produced  Ls  identical  with 
tetanus  by  faradization. 


126  THE  MYOGRAPH. 

10.  Chemical  Excitation.— Make  a  nerve-muscle  preparation.  Place 
it  on  a  card,  having  a  hole  in  the  middle  just  large  enough  to  allow  the  nerve 
to  pass.  Place  the  card,  with  the  nerve  hanging  from  it,  over  a  beaker  con- 
taining ammonia.  The  muscle  does  not  contract.  Then  cut  off  the  nerve 
and  expose  the  muscle  to  thegas.  It  contracts.  Glycerine,  on  the  other  hand, 
excites  nerve  readily,  but  scarcely  acts  on  muscle. 

11.  Action  of  the  Arrow  Poison   (Curare)  on  Muscle 

and.  Nerve. — in  a  preparation  of  which  the  hemispheres  have  been 
destroyed,  pass  a  ligature  under  the  sciatic  nerve  above  one  knee  and  tighten 
it  so  as  completely  to  arrest  the  circulation  beyond.  Inject  a  drop  of  a  solu- 
tion containing  o"i  per  cent  of  curare  under  the  skin  and  leave  the  preparation 
in  a  moist  chamber  for  an  hour.  Then  test  the  condition  of  the  muscles  by 
direct  excitation  and  excite  both  sciatic  nerves,  comparing  the  effects.  Although 
both  have  been  equally  acted  upon,  it  is  on  the  ligatured  side  only  that  the 
excitation  is  responded  to.  The  experiment  shows  that  the  arrow  poison  acts 
neither  on  nerve  trunks  nor  on  muscular  tissue  but  only  on  the  muscular 
nerve-endings. 

II. — The  Myog)-aph. 

Any  insti-ument  by  which  a  curve  can  be  drawn  which  truly  represents  the 
contraction  of  a  muscle  is  called  a  myograph. 

I.  The  most  simple  myograph  is  that  of  Marey,  the  construction  of  which 
is  as  follows : — A  pillar,  supported  by  the  horizontal  triangular  bar  of  the  record- 
ing apparatus  (kymograph),  carries  a  board  seven  inches  long  by  two  and  a 
half  in  width,  which  with  the  aid  of  a  rack-and-pinion  and  adjusting  screw, 
can  be  moved  either  vertically  or  horizontally.  At  one  end  of  the  board  is  a 
vertical  pillar  on  which  a  writing  lever  is  supported  ;  the  point  of  the  lever 
can  be  brought  into  such  a  position  as  to  inscribe  its  movements  on  the 
revolving  cylinder.  The  lever  is  centred  on  a  horizontal  axis,  its  motion  being 
resisted  by  a  delicate  spring.  The  upper  surface  of  the  board  is  covered  to 
within  a  short  distance  from  the  lever,  with  a  thick  plate  of  cork.  (See 
"  Handbook,"  fig.  270  bis.) 

Various  muscles  of  the  frog  are  used  for  myographic  purposes  ;  the  one 
most  easily  prepared  is  the  gastrocnemius.  All  that  is  required  is  to  divide 
the  skin  so  as  to  expose  the  tendon,  and  to  attach  the  latter  to  a  strong  liga- 
ture thread.  A  strong  needle  must  now  be  thmst  through  the  end  of  the 
femur  without  injuring  other  parts,  so  as  to  fix  the  femoral  attachment  of  the 
muscle  to  the  cork  plate  in  such  a  position  that  the  ligature  may  be  advan- 
tageously fastened  to  the  lever. 

Arrange  the  apparatus  for  single  induction  shocks  as  directed  in  Section  I.,  2, 
interposing  in  the  primaiy  circuit  an  additional  key,  which  is  so  placed  as  to  be 
opened  by  the  recording  cylinder  on  arriving  at  a  certain  part  of  its  revolution. 

Cover  the  cylinder  smoothly  and  tightly  with  glazed  paper,  taking  care  that 
the  edge  of  the  crease  does  not  catch  the  writing  style.  Smoke  the  surface 
uniformly  with  a  paraffin  lamp  and  put  the  cylinder  on  the  middle  axis. 

Place  the  electrodes  on  the  tongue  and  set  the  clock  in  motion,  so  as  to 
ascertain  that  the  electrical  apparatus  is  working  properly. 


THE  MYOGRAPH.  12/ 

2.  The  Curve  of  a  Single  Contraction,  or  Twitch.— Pith  a 

frog  and  place  it  on  its  belly  on  the  myograph  plate.  After  preparing  and 
attaching  the  muscle  as  above  directed,  expose  the  sciatic  nerve,  and  place  the 
electrodes  under  it.  Adjust  the  style  of  the  lever  so  as  to  touch  the  smoked 
surface.  Open  the  key  of  the  primary  circuit  and  set  the  clock  in  motion. 
A  line  is  drawn  by  the  style — the  abscissa  of  the  future  curve.  As  soon  as 
the  fly  has  attained  its  maximum  expansion,  close  both  keys  of  the  primary 
circuit.  At  the  moment  the  cylinder  comes  into  contact  with  its  key  and 
opens  it,  a  curve  is  inscyribed.  Stop  the  clock  and  prepare  for  a  second  obser- 
vation by  giving  a  single  or  half  turn  to  the  pinion,  and  draw  a  second  curve 
similar  to  the  first,  and  so  on,  until  a  series  of  parallel  and  similar  curves  has  been 
drawn.  To  observe  the  effect  of  exhaustion  arrange  the  apparatus  so  that,  while 
the  muscle  is  excited  at  each  revolution,  every  tenth  curve  only  is  recorded. 

3-  Influence  of  Veratrin. — inject  a  drop  of  o*i  per  cent,  solution 
of  Veratrin  into  the  lymph  sac  of  a  brainless  frog.  After  twenty  minutes, 
destroy  the  spinal  cord  and  inscribe  one  or  more  muscle  curves,  and  compare 

hem  with  those  previously  obtained. 

If  in  this,  and  in  the  preceding  experiment,  it  be  desired  to  employ  the  "nerve- 
muscle  preparation  "  rather  than  the  entire  pithed  frog,  the  apparatus  described 
below  may  be  substituted  ;  it  can  be  made  with  simple  materials,  such  as  can 
be  procured  anywhere.  A  thick  brass  wire  is  bent  twice  at  right  angles,  in 
the  same  plane.  The  middle  part  measures  four  inches,  and  each  of  the  ends 
two  inches.  On  the  middle  part  slides  a  cork  bearing  two  centres,  in  which  . 
an  axis  works.  This  axis  bears  a  light  lever  about  five  inches  long,  which 
moves  in  the  plane  of  the  two  ends.  The  femur  of  the  muscle-nerve  prepara- 
tion is  attached  by  a  wire  to  the  upper  end  of  the  brass  wire  (called  the 
stretcher),  and  the  tendon  to  the  lever.  A  spiral  spring,  connecting  the  lower 
end  of  the  stretcher  with  the  lever,  serves  to  extend  the  muscle  and  opposes 
its  contraction.  The  nerve  is  enclosed  in  a  tube  provided  with  platinum  elec- 
trodes, which  serves  to  protect  it  from  evaporation.  The  whole  apparatus  is 
supported  as  before  (II,  i),  on  an  adjustable  pillar,  which  is  fixed  to  the 
recording  apparatus. 

4-  Influence  of  Temperature  on  the  Form  of  the  Curve  of  Single 
Contraction. — For  studying  this  suliject,  the  simple  myograph  just  described 
may  be  used.  A  spiral  tube  of  metal  of  suitable  form,  must  be  prepared 
and  fixed  to  the  stretcher  so  as  to  surround  the  muscle  during  the  observation. 
One  end  of  the  coil  is  connected  by  a  flexible  tube  with  a  small  reservoir  of 
water  at  a  higher  level,  the  other  with  a  waste  pipe.  Make  a  muscle-nerve 
preparation,  pierce  the  femur  with  a  fine  awl,  and  pass  a  fine  wire  through 
the  hole  and  attach  it  to  the  upper  arm  of  the  stretcher.  Secure  the  tendon 
by  a  ligature  to  the  lever  and  adjust  the  spiral  spring,  so  that  the  lever  is 
parallel  to  the  arms  of  the  stretcher.  AVith  the  aid  of  a  fine  silk  thread 
tied  to  its  end,  introduce  the  nerve  with  great  care  into  the  electrode  tube  and 
close  the  latter  with  its  cork.     Adjust  the  writing  lever. 

Having  made  the  same  arrangement  as  in  the  last  exercise,  pass  a  stream  of 
water  through  the  coil  at  the  ordinary  temperature  and  inscribe  a  succession  of 
curves.  Then  repeat  the  observation,  passing  water  through  at  various  tem- 
peratures from  5°  C.  to  30'  C,  observing  the  successive  alterations  in  the  form 
of  the  contraction  curve. 


128  THE   MYOGRAPH. 

5-  The  Curve  of  TetamiS- — Arrange  the  apparatus  (as  directed  in 
Section  I.  2)  for  single  induction  shocks.  Introduce  into  the  primary  circuit 
a  reed  which  automatically  makes  and  breaks  the  circuit  twenty  times  in  a 
second.  Prepare  and  fix  the  muscle  according  to  either  of  the  methods 
described  above.  On  closing  the  key  of  the  primary  circuit  for  ten  seconds, 
the  muscle  is  tetanized  and  the  curve  inscribed  on  the  cylinder  {see  p.  56). 

Arrange  the  induction  apparatus  for  faradization  (see  Section  I.  I,b),  and 
repeat  the  preceding  obsei-vation. 

6.  The  Time-Relations  of  a  Muscular   Contraction.— 

I.  By  noting  the  time  required  for  a  sufficient  number  of  revolutions  of  the 
recording  cylinder  and  accurately  measuring  its  circumference,  the  rate  of 
movement  of  the  recording  surface  may  be  determined,  and  thereby  the 
time-value  of  the  records  known.  2.  A  more  direct  method  is  to  write 
simultaneously  under  the  tracing  the  oscillations  of  a  tuning-fork  of  which 
the  vibration-rate  is  known.  For  this  purpose  the  tuning-fork  may  be 
made  to  inscribe  its  vibrations  directly,  or  (more  conveniently)  it  may 
be  introduced  into  a  battery  circuit,  so  as  to  interrupt  it  at  each  vibra- 
tion. An  electromagnetic  writer  (chronograph)  is  introduced  into  the  same 
circuit ;  it  vibrates  synchronously  with  the  fork,  and  reproduces  its  motions 
on  the  cylinder.  Record  a  curve  of  single  contraction,  usiiig  the  "  stretcher," 
and  fix  the  recording  cylinder  on  the  quick  axis.  Mark  the  point  of 
excitation  by  bringing  the  trigger  of  the  cylinder  veiy  slowly  into 
contact  with  the  lever  of  the  key.  Measure  the  distances  from  the  point, 
— (i)  to  the  beginning  of  the  curve,  (2)  to  its  maximum,  and  (3)  to  its  close, 
and  determine  their  value  by  either  of  the  methods  given  above. 

7.  Measurement  of  the  Period  of  Latent  Stimulation  and  of 
the  Rate  of  Propagation  in  Nerve,  by  the  Pendulum  Myograph.— 
Preparation  of  the  Apparatus.  Cover  the  glass  plate  smoothly  with  paper, 
smoke  its  surface  as  before,  and  fix  it  to  the  pendulum.  Arrange  the 
"trigger"  and  the  "catch  "so  that  the  pendulum  when  detached  from  the 
former  just  catches  on  the  latter.  Test  the  instrument  by  taking  tracings 
with  a  tuning-fork  vibrating  100  times  a  second,  on  the  smoked  paper,  when 
the  pendulum  is  moving  at  several  different  velocities  (the  velocity  varying 
with  the  positions  of  the  trigger  and  catch).  Arrange  the  electrical  apparatus 
for  single  shocks  as  in  Sect.  I,  2,  including  in  the  primary  circuit  one  of  the 
keys  of  the  myograph.  Prepare  the  gastrocnemius  as  in  Sect.  II,  l.  Fix 
the  femur  firmly  to  the  cork  table,  pass  the  ligature  round  the  pulley  and 
attach  it  to  the  lever,  adjusting  the  spiral  spring  to  a  suitable  strength.  Take 
great  care  that  no  part  of  the  apparatus  touches  the  glass  plate,  as  the  pen- 
dulum swings.  Arrange  the  lever  very  carefully,  so  that  when  it  is  brought 
into  position  by  the  rotating  handle  it  writes  on  the  smoked  surface.  Observe 
that  the  glass  plate  is  so  adjusted  that  the  lever  at  first  touches  it  lightly,  but 
presses  more  strongly  as  the  plate  swings  past.  Catch  the  pendulum  with 
the  trigger,  see  that  everything  is  in  order — the  keys  closed,  the  lever  in  its 
position,  the  electrodes  under  the  nei-ve,  etc.  On  liberating  the  pendulum,  a 
muscle  curve  is  inscribed  on  the  smoked  surface.  Withdraw  the  lever  from 
its  writing  position,  bring  the  pendulum  back  past  the  key,  close  the  latter, 
keeping  it  closed  by  firm  pressure  of  the  finger,  allow  the  pendulum  to  rest 
against  it,  bring  the  lever  into  the  writing  position,  and  make  a  mark  on  the 


THE   FROG    HEART.  I29 

surface,  which  indicates  the  moment  of  excitation.  Take  three  or  four  similar 
curves,  depressing  the  table  an  equal  distance  after  each  observation  (^  or  4 
turn)  by  Die  handle.  Remove  the  muscle  lever  and  take  a  tracing  with  a  tuning- 
fork,  vibracing  100  times  a  second,  carefully  arranging  the  style  of  the  fork  in 
the  position  previously  occupied  by  the  writing  end  of  the  muscle  lever. 
Remove  the  paper,  varnish  and  measure  the  tracings.  From  the  mean  result 
of  the  measurements,  the  latent  stimulation  may  be  computed. 

8.  Rate  of  Propagation-  —  i-  Prepare  the  muscle  as  in  the  last  exercise. 
Expose  the  sciatic  nerve  throughout  its  length.  Place  one  pair  of  electrodes 
under  the  nerve  close  to  the  muscle,  and  a  second  pair  under  the  nerve  near  its 
origin.  Connect  these  two  pairs  of  electrodes  with  a  switch.  To  the  middle 
screws  of  the  switch  attach  the  wires  from  the  secondary  coil,  so  that  by  turn- 
ing over  the  bridge  of  the  switch,  the  near  and  the  distant  portion  of  the 
nerve  can  be  excited  alternately  without  loss  of  time.  The  nerve  should  be 
prepared  with  great  care,  and  each  exposed  part  should  be  protected  by  a  flap 
of  muscle,  except  at  the  moment  that  it  is  being  excited.  Take  tracings  of 
muscle  curves  in  pairs,  alternately  exciting  the  near  and  distant  portions  of  the 
nerve.  Take  a  tuning-fork  tracing,  varnish,  measure  the  length  of  nerve 
from  one  pair  of  electrodes  to  the  other,  and  therefrom  determine  the  rate  of 
propagation  in  the  nerve  (see  p.  77). 


Ul.  —  T/te  Frog  Heart. 

1.  Rhythmical  Motions- — in  a  curarized  preparation  of  which  the 
hemispheres  have  been  destroyed,  expose  the  sternum  and  cut  across  the 
episternal  cartilage.  Then  sever  the  sternum  from  its  connections  by  a  cut  on 
either  side,  and  turn  it  down  over  the  belly.  The  heart  is  seen  still  covered 
by  the  pericardium.  Expose  the  heart  by  carefully  dividing  the  peri- 
cardium. Note  the  condition  of  each  of  its  cavities  and  the  mode  of  its 
rhythmical  action. 

2.  The  Inhibitory  Centre.— For  the  purpose  of  observing  the  effect 
of  passing  series  of  induction  shocks  through  the  inhibitory  centre  of  the 
heart,  a  fine  ligature  is  attached  to  the  fra2num  (the  thread-like  ligament  which 
stretches  from  the  dorsal  aspect  of  the  ventricle  towards  the  lower  part  of  the 
pericardium).  By  means  of  the  ligature  the  heart  is  raised  out  of  its  place 
and  turned  upwards.  The  inhil)itory  centre  is  recognized  by  the  whitish 
crescent-shaped  line  which  marks  the  junction  of  the  wall  of  the  sinus  with 
that  of  the  right  auricle.  Faradize  this  spot  for  a  second  or  less,  placing  the 
points  of  the  electrodes  on  the  line,  a  couple  of  millims.  distant  from  each 
other.  Observe  the  mode  and  order  in  which  the  cavities  of  the  heart  resume 
their  rhythmical  action. 

3.  Destroy  the  spinal  cord  by  pithing,  and  observe  the  changes  thereby 
produced  in  the  state  of  the  circulation,  and  particularly  in  the  mode  of  action 
of  the  heart. 

4-  The  Cardiac  Vagus  of  the  Frog.— <?.  Preliminary  Dissection.— 
Expose  the  trunk  of  the  vagus  nerve  as  it  escapes  from  the  cranium  as  follows  : — 
Remove  the  integument  so  as  to  bring  into  view  the  muscles  of  the  back  of 

K 


I30  THE   FROG   HEART. 

the  neck  on  one  side,  avoiding  injury  to  the  cutaneous  vessels.  Tiien  expose 
the  scapula,  and  sever  with  the  scissors  the  cartilaginous  from  the  bony 
scapula ;  remove  the  former,  dividing  the  muscles  attached  to  it,  then  expose 
the  sterno-mastoid  muscle  which  connects  the  outer  part  of  the  petrous  bone 
and  the  posterior  border  of  the  cartilaginous  ring  of  the  membrana  tympani 
with  the  concave  anterior  border  of  the  scapula.  Remove  or  draw  aside  the 
sterno-mastoid  so  as  to  expose  the  slender  muscles  (petrohyodei)  v/hich  run  from 
the  petrous  bone  to  the  posterior  horn  of  the  hyoid  bone,  embracing  the 
cavity  of  the  pharynx.  Parallel  with  these  muscles,  and  in  close  relation  with 
them,  are  seen  the  carotid  artery  and  several  nerves,  of  which  the  two  nearest 
the  cranium  are  the  glosso-jjliaryngeal  and  the  vagus. 

b.  Expose  the  vagus  in  a  pithed  preparation.  Expose  the  heart  as  in  III.  I, 
and  introduce  a  small  test  tube  into  the  gullet.  Fix  the  preparation  in  such  a 
position  on  a  cork,  that  the  electrodes  can  be  conveniently  applied  to  the  nerve, 
at  the  same  time  that  the  motion  of  the  heart  can  be  observed. 

5.  The  Stannius  Heart. — Prepare  a  frog  heart  with  frsenum  ligature 
as  before.  Then  pass  a  thick  ligature  under  the  bifurcation  of  the  aorta 
between  it  and  the  venae  cavce  superiores.  Then,  seizing  the  frsenum  ligature 
with  the  forceps,  turn  the  heart  up.  Carefully  observe  the  position  of  the 
' '  crescent, "  and  loop  the  ends  of  the  ligature  so  that  when  it  is  tightened  it 
may  embrace  the  crescent.     On  tightening,  the  heart  will  stop  in  diastole. 

In  the  heart  so  prepared,  sever  the  ligatured  parts  from  the  rest  of  the  pre- 
paration with  sharp  scissors.  The  aui"icles  and  ventricle  resume  their  normal 
rhythmical  action. 

Cut  off  in  a  preparation  which  has  been  so  treated,  the  remainder  of  the 
auricles  and  the  bulb,  leaving  the  ventricle  and  auriculo-ventricular  septum. 
The  heart  continues  to  beat  normally,  or,  if  the  beats  cease,  they  are  renewed 
by  a  pinch,  by  an  induction  shock,  or  by  bringing  a  hot  wire  into  the  neigh- 
bourhood of  the  cut  surface. 

6.  Localization  of  the  Motor  Centres.— In  one  of  two  such  pre- 
parations (called  ventricle  preparations)  which  beat  rhythmically,  cut  off  the 
whole  of  the  auriculo-ventricular  furrow  with  sharp  scissors.  The  preparation  so 
obtained  (the  ventricle  apex)  does  not  contract  spontaneously,  but  responds  to  a 
single  excitation,  whether  mechanical  or  electrical,  by  a  single  contraction,  the 
duration  of  which  is  dependent  on  the  temperature.  In  the  other  preparation, 
divide  the  ventricle  by  two  parallel  cuts  into  a  middle  and  two  lateral  thirds.  The 
middle  third  includes  the  ventricular  border  of  the  interauricular  septum,  the 
right  lateral  third  contains  the  root  of  the  bulb.  The  middle  third  beats 
rhythmically,  the  lateral  th.irds  respond  to  excitations  by  single  contractions, 
but  do  not  beat  of  themselves. 

7.  Action  of  Muscarin  and  Atropin.— In  an  entire  heart  (a 
heart  removed  by  severing  the  vessels,  for  which  purpose  the  organ  should  be 
lifted  out  of  the  pericardium  by  a  ligature  tied  to  the  froenum),  stop  rhythmical 
action  by  applying  to  it  a  drop  of  serum  containing  a  trace  of  muscarin. 
Observe  the  relaxed  and  motionless  condition  of  the  ventricle.  After  a  few 
minutes  apply  (in  serum)  a  drop  of  0*2  percent,  solution  of  atropin.  Obsei-ve 
the  gradual  restoration  of  rhythmical  action  in  theatropinized  heart.  Observe 
that  faradization  of  the  inhibitory  centre  is  without  effect. 


TlIK   FROG   HEART.  I3I 

8.  Action  of  the  Constant  Current  on  the  Contractile 

Substance  of  the  Heart. — For  tliis  purpose  prepare  electrodes  as 
directcil  in  Exorcise  I.  Fix  a  cork  vertically  on  a  sheet  of  lead  about 
an  inch  and  a  half  square  ;  cover  the  top  of  the  cork  with  wax  mass,  the 
upper  surface  of  which  should  be  somewhat  concave.  Place  the  support 
on  a  sheet  of  wet  fdtering  paper  and  cover  it  with  a  beaker.  Attach  a  fine 
ligature  to  the  frx'num,  and  remove  the  heart  after  severing  the  principal 
vessels.  Collect  some  blood  and  dilute  it  with  as  much  075  per  cent,  salt 
solution,  and  place  a  few  drops  of  it  on  the  wax  surface. 

Make  a  "ventricle-apex  preparation,"  as  directed  in  6.  Having  ascertained 
that  it  does  not  beat  rhythmically  of  itself,  fix  it  in  its  place  by  the  aid  of 
fine  glass  pins  and  replace  the  beaker. 

Prepare  and  arrange  two  Grove's  cells  in  circuit,  interpose  a  key  and  a 
pair  of  electrodes.  Fix  the  electrodes,  so  that  their  points  are  in  contact  with 
the  apex  and  base  respectively  of  the  preparation.  The  passage  through  the 
ventricle  apex  of  a  voltaic  current  in  the  direction  of  its  axis  produces 
rhythmical  action,  which  lasts  as  long  as  the  current  passes. 

9-  Study  of  the  Ventricular  Systole  by  the  Graphical 

Method. — Prepare  a  writing  lever  consisting  of  a  glass  rod  about  ^'g  inch 
in  thickness  and  five  inches  long,  having  at  one  end  a  knob  of  glass,  and  at 
the  other  a  writing  point.  This  is  thrust  through  a  square  bit  of  cork,  which  is 
then  pushed  up  to  the  knob.  A  fine  steel  needle  passes  through  the  cork  at 
right  angles  to  the  rod.  The  rod  also  bears,  close  to  the  needle,  a  vertical  arm 
of  cork,  by  means  of  which  it  rests  on  the  ventricle.  The  preparation  lies  on 
a  metal  plate,  which  forms  the  upper  end  of  a  cylindrical  bra.ss  box,  through 
which  water,  at  any  desired  temperature,  can  be  passed.  This  plats  is  furnished 
with  bearings  in  which  the  steel  axis  of  the  lever  works.  The  metal  box  is 
fixed  to  one  of  the  adjustable  supports  of  the  recording  apparatus. 

a.  The  rhythmically  contracting  heart. 

Expose  the  heart  as  before.  Raise  it  from  the  pericardium  by  a  ligature 
attached  to  the  severed  frrenum,  and  cut  through  the  vessels.  Place  the  heart 
on  the  plate,  adding  a  few  drops  of  dilute  serum,  and  arrange  the  lever  so  that 
the  cork  arm  rests  on  the  ventricle,  and  the  writing  end  inscribes  its  move- 
ments on  the  blackened  surface  of  the  cylinder.  The  rate  of  motion  should 
be  about  20  inches  per  minute. 

Allow  water  at  12°  C.  to  pass  through  the  cylindrical  box  and  record  the 
rhythmical  contractions  of  the  ventricle.  Repeat  the  experiment,  substituting 
water  at  17°  and  at  22',  and  compare  the  tracings. 

6.  The  curve  of  a  single  ventricular  contraction. 

Prepare  finely  pointed  electrodes  as  in  I.  i,  arranging  for  single  induction 
shocks.  Fix  the  electrodes  to  an  .adjustable  support,  so  that  they  can  be 
brought  with  precision  into  contact  with  the  preparation.  Prepare  a  Stannius' 
heart  and  arrange  it  for  recording  as  in  a.  Adjust  the  electrodes,  taking  care 
not  to  interfere  with  the  lever.  Place  the  secondary  coil  at  about  10  centimeters 
distance  from  the  primary,  or  nearer,  if  on  trial  it  is  found  necessary  to  do  so, 
Then  bring  the  point  of  the  lever  into  contact  with  the  blackened  paper,  so 
as  to  write  a  base  line  or  abscissa,  and  open  the  key.  The  rate  of  motioa 
of  the  recording  surface  should  be  about  2i  inches  jier  second. 

K   2 


132  FUNCTIONS   OF   REFLEX   CENTRES. 

In  order  to  obtain  series  of  tracings  which  can  be  conveniently  compared, 
introduce  into  the  primary  circuit  the  self-acting  key  described  in  II.  i.  In 
this  way  a  number  of  curves  may  be  drawn  on  the  same  abscissa,  or  on 
parallel  abscissae  at  convenient  distances  from  each  other.  Having  practised 
one  or  other  of  these  methods,  proceed  to  make  the  following  observa- 
tions : — 

(i.)  When  a  succession  of  ventricular  curves  are  drawn  at  temperatures 
varj'ing  from  12°  to  1 8°,  it  is  found  that  the  duration  of  the  systole  is  increased 
by  about  o"'i  for  every  degree  of  temperature. 

(2.)  When  the  ventricle  is  excited  by  single  induction  shocks,  following  each 
other  at  about  lo"  intervals,  each  curve  is  observed  to  exceed  its  predecessor 
in  amplitude,  the  augments  gradually  diminishing  from  the  beginning  to  the 
end  of  the  series. 

(3.)  In  the  muscular  tissue  of  the  heart,  the  period  of  latent  stimulation  is 
much  longer  than  in  voluntary  muscle.  Its  duration  is  about  o"*i5.  To  measure 
it,  a  vertical  line  must  be  drawn  on  the  recording  surface,  indicating  the  position 
of  the  writing  point  at  the  moment  that  the  trigger  of  the  cylinder  comes  into 
contact  with  the  lever  of  the  self-acting  key  (see  II.  i). 


IV. — Functions  of  the  Spinal  and  other  Reflex  Centies  of  the  Fro^. 

1.  The  preparation  to  be  used  in  the  following  experiments  is  obtained  by 
severing  the  spinal  cord  immediately  behind  the  medulla  oblongata  and  intro- 
ducing, by  the  opening  made  for  this  purpose,  a  wooden  plug  into  the  cranial 
cavity,  so  as  to  destroy  its  contents.  This  having  been  done,  it  is  placed  on  a 
sheet  of  moist  filter-paper,  resting  on  its  ventral  surface  with  the  hind  limbs 
extended,  and  covered  with  a  bell  jar.  For  a  time  it  remains  motionless,  but 
eventually  assumes  a  position  which  differs  but  little  from  that  of  a  living  frog. 
Observe  the  differences. 

2.  Prepare  half-a-dozen  pieces  of  filter-paper,  each  an  eighth  of  an  inch 
square,  and  some  strong  acetic  acid.  Turn  the  preparation  over,  and  after 
observing  that  the  natural  position  is  not  resumed,  apply  one  of  the  squares, 
after  moistening  it  with  acetic  acid  and  drawing  off  excess  by  touching  with 
dry  filter-paper,  to  the  inside  of  the  right  thigh,  and  observe  the  result. 
Repeat  the  experiment,  holding  the  right  foot.  Next,  attach  the  preparation 
to  a  suitable  holder  in  such  a  way  that  the  trunk  may  be  steadily  supported 
and  the  limbs  may  hang  freely,  and  apply  the  squares  in  succession  to  different 
parts  of  the  surface,  as  e.g.,  to  the  skin  on  either  side  of  the  tendo  Achillis,  or 
to  either  flank.  Observe  in  each  case  that  the  muscular  response  which 
results  from  excitation  of  the  same  part  of  the  surface  of  the  body  is  always 
the  same. 

3.  Arrange  a  second  preparation  as  last  described,  using  a  holder  so  con- 
structed that  the  limbs  may  be  suspended  at  any  desired  height  above  the 
table.  Prepare  several  beakers  of  water  acidulated  respectively  with  i,  2,  3, 
4  and  5  per  thousand  of  sulphuric  acid,  and  place  some  of  each  mixture  in 
a  saucer.  Beginning  with  the  weakest  of  the  acid  liquids,  bring  down  the 
preparation  with  the  rack  and  pinion,    until  the  tip  of  the  longest  toe  is 


SENSATION   AND   PERCEPTION.  1 33 

immersed.  Repeat  the  experiment  at  intervals  of  three  minutes  with  the 
stronger  liquids  in  order,  carefully  washing  the  foot  after  each  excitation,  by 
tlipping  it  into  a  beaker  of  water.  Measure  the  time  which  intervenes 
between  the  beginning  of  the  excitation  and  the  muscular  response  in  each 
case,  with  the  aid  of  a  metronome. 

4.  Observe  carefully  the  attitude  of  a  brainless  frog  when  left  to  itself,  and 
its  behaviour  when  placed  on  its  back,  on  an  inclined  surface,  or  in  water,  as 
well  as  when  excited  by  cutaneous  stimuli,  comparing  the  phenomena  observed 
with  those  which  exhibit  themselves  in  the  spinal  cord  preparation. 

5.  Proceed  as  in  i,  substituting  a  preparation  in  which,  after  destruction 
of  the  brain,  a  couple  of  drops  of  a  0"i  percent,  solution  of  sulphate  of  strychnia 
have  been  injected  under  the  skin  of  the  back.  Observe  that  instead  of 
co-ordinate  muscular  responses,  cutaneous  excitation  produces  under  the  influ- 
ence of  strychnia,  paroxysms  of  convulsion,  in  which  the  body  and  limbs 
assume  a  characteristic  attitude. 


V. — Sensation  and  Perception. 

1.  Time  Occupied  in  the  Simplest  Mental   Processes 

•{see\),  104). — To  measure  the  time  required  for  responding  to  a  signal  (re- 
action time  or  personal  time),  the  simplest  plan  is  to  arrange  a  battery  circuit 
in  such  a  way  that  it  is  closed  by  the  same  act  by  which  the  observer  makes 
the  signal,  and  that  it  is  opened  by  the  response  of  the  observed  per- 
son. Whatever  be  the  nature  of  the  signal,  the  requirements  are:  (i)  Two 
Grove's  cells  arranged  in  circuit;  (2)  a  break  key  (a  lever  resembling  in  shape 
a  pianoforte  key,  which  when  touched  breaks  a  mercurial  contact) ;  (3)  a 
du  Bois'  key ;  (4)  an  electro-magnet  with  a  light  lever  attached  to  its  arma- 
ture ;  (5)  a  chronograph  ;  (6)  a  recording  surface,  of  which  the  rate  of  motion 
is  not  less  than  i  foot  per  second.  The  batter)',  two  keys,  electro-magnet 
and  chronograph,  are  arranged  in  circuit,  and  in  such  positions  that  the  electro- 
magnet lever  may  be  in  the  neighbourhood  of  the  observed  person,  and  the 
du  Bois'  key,  cylinder  and  chronograph,  in  reach  of  the  observer.  On 
closing  the  circuit,  the  lever  is  drawn  towards  the  magnet  and  gives  the  signal. 
The  signal  may  be  an  induction  shock  through  the  tip  of  the  tong\ie  (in 
-which  case  an  induction  coil  must  be  in  circuit  in  addition  to  the  instruments 
above-mentioned),  a  touch  on  the  hand  given  by  the  lever,  a  sound  or  a  visible 
signal,  such  as  a  white  disk,  letter  or  number,  suddenly  brought  into  view. 

2.  Tactile   and  Muscular  Sensation.— in  all  the  following 

experiments  two  persons  must  take  part  :  one  of  whom  must  vary  the  condi- 
tions without  the  knowledge  of  the  other,  and  note  the  results.  In  the  experi- 
ments relating  to  the  sensations  of  pressure,  locality,  and  muscular  exertion, 
the  observed  person  must  have  his  eyes  shut. 

The  appreciation  of  Temperature  must  be  tested  by  immersing  the 
same  surface  successively  in  water  of  slightly  different  temperatures.  The 
smallest  differences  can  be  detected  when  the  temperatures  of  the  liquids  com- 
pared approximate  30°  C. 

To  test  the  sensation  of  Pressure,  the  hand  or  other  part  to  be  investi- 


134  VISION. 

gated  must  be  entirely  at  rest,  and  supported  on  a  horizontal  surface.  The 
weights  used  must  be  moderate — from  a  pound  to  four  or  five  pounds ;  in 
which  case  it  will  be  found  that  a  difference  between  two  weights  of  one- 
thirtieth  can  be  detected. 

For  testing  the  sensation  of  locality  in  any  part  of  the  surface  of  the 
body,  a  pair  of  compasses  is  used,  of  which  the  points  are  provided  with  cork 
sheaths,  having  smooth  blunt  ends.  The  points  being  at  first  at  such  a  dis- 
tance that  when  both  touch  the  skin  or  mucous  membrane  of  the  tongue, 
they  are  distinctly  felt  as  two,  they  are  gradually  brought  nearer  until  the  two 
impressions  blend  into  one.  The  smaller  the  distance  at  which  this  happens, 
the  finer  is  the  sensation  of  locality  in  the  region  investigated.  Another 
method  is  that  of  interrogation.  The  observer  touches  the  skin,  and  asks  the 
observed  person  to  designate  the  locality  touched. 

The  sensation  of  mUSCUlar  Exertion  is  tested  by  experiments, 
each  of  which  consists  in  lifting  in  succession  two  weights,  of  which  one  is 
heavier  than  the  other  by  a  small  but  perceptible  difference  ;  this  difference  is 
diminished  at  each  trial  until  it  can  no  longer  be  appreciated.  As  it  is  essential 
that  sensation  of  pressure  should  be  excluded,  the  weight  to  be  estimated, 
must  in  each  trial  be  enclosed  in  a  handkerchief,  of  which  the  corners  must 
be  held  in  the  hand. 

For  the  investigation  of  the  sensation  of  taste  and  of  the  limits  of  the 
gustatory  region,  four  test  liquids  should  be  prepared,  viz, ,  saturated  solution 
of  sulphate  of  quinine,  lo  per  cent,  solution  of  common  salt,  3  per  cent, 
solution  of  sugar,  and  o'l  per  cent,  solution  of  citric  acid.  These  liquids 
represent  the  four  fundamental  sensations,  each  of  which  may  be  tested 
separately,  or  two  alternately.  In  each  experiment  a  camel  hair  pencil  is 
dipped  in  the  liquid,  drained  by  touching  it  with  filter  paper,  and  applied  for 
a  moment  to  the  surface.  To  secure  freedom  from  bias  on  the  part  of  the 
observed  person,  trials  should  be  made  in  which  tasteless  liquids,  or  liquids 
of  different  tastes  are  alternated  in  various  orders,  care  being  taken  to  irrigate 
the  surface  between  each  trial  and  the  following  one,  with  water. 

The  voltaic  sensations  of  taste  are  experienced  when  two  zinc  plates,  which 
form  the  terminals  of  a  Grove's  element,  are  applied  respectively  to  the  upper 
and  under  surface  of  the  tongue  as  far  back  as  possible.  As  the  effect  differs 
according  to  the  direction  of  the  current,  a  reversing  key  must  be  introduced 
into  the  circuit. 


VI.  — Vision.  * 

I.  The  application  of  Scheiner's  experiment  to  the  limitation  of 
the  range  of  accommodation  can  be  best  understood  if  it  is  made  as  follows : — 
Stretch  a  white  thread  from  end  to  end  along  the  blackened  surface  of  a  narrow 
black  board  about  a  yard  long.     Fix  at  one  end  of  the  board  a  vertical  screen 

*  The  experiments  and  observations  described  under  this  heading  are 
arranged  in  the  order  in  which  the  subjects  they  are  intended  to  illustrate 
happen  to  be  referred  to  in  the  lectures. 


VISION.  135 

or  diaphragm,  having  two  vertical  and  parallel  slits,  about  three  millims. 
apart,  taking  care  that  the  slits  arc  opposite  the  thread,  \Vhen  the  thread  is 
contemplated  through  the  slits,  by  a  normal  or  myopic  eye  accommodated  for 
near  vision,  two  white  lines  are  seen,  which  converge  towards  the  spot  in  the 
thread,  for  the  distinct  vision  of  which  the  eye  is  accommodated,  and,  after 
crossing,  diverge.  If  the  eye  were  hypermetropic,  the  lines  would  not  con- 
verge even  if  accommodated  to  the  utmost. 

2.  Sanson's  or  Purkinje's  images.— The  relative  positions  of  the 
observed  and  observing  eye,  and  of  the  luminous  object,  which  are  most 
advantageous  for  the  observation  of  the  image  reflected  by  the  anterior  surface 
of  the  lens,  are  stated  on  page  loS.  The  experiment  must  be  made  in  a  dark 
room.  It  is  advantageous  to  substitute  two  lights,  one  above  the  other,  for 
the  single  luminous  object  referred  to  in  the  text. 

3-  Chromatism.— In  order  to  see  the  effects  described  in  the  text 
(p.  109)  it  is  advantageous  to  place  before  the  eye  a  purple  glass,  which,  by 
cutting  off  the  rays  of  medium  refrangibility,  facilitates  the  perception  of  the 
red  and  blue  rays. 

4-  Reflection  of  light  from  the  Retina  (sec  p.  109).— To  see 

the  eye  of  another  person  luminous,  the  simplest  way  is  to  inlerpoee  between 
the  observed  and  the  observing  eye  a  reflector,  consisting  of  several  glass 
plates  applied  to  each  other  by  their  surfaces,  in  such  a  position  that  the  light 
of  a  lamp  placed  on  one  side  of  the  observed  eye  may  be  seen  by  it.  The 
moment  that  this  is  the  case,  the  retina  is  illuminated  ;  and  if  the  observed 
eye  is  accommodated  for  distinct  vision  of  the  lamp  flame,  and  a  suitable 
concave  lens  placed  in  front  of  the  observing  eye,  a  distinct  image  of  the 
flame  is  seen  on  the  observed  retina,  the  whole  interior  of  the  globe  appearing 
at  the  same  time  luminous. 

5.  The  Fovea  Centralis  (see  p.  no).— (a)  Fix  a  blackboard  hori- 
zontally at  a  level  a  little  below  that  of  the  eyes.  Mark  a  point  a  at  one  edge 
of  the  board,  and  bring  the  right  eye  up  to  it,  closing  the  other,  and  plant  a 
pin  having  a  white  bead  for  its  head  in  the  board  at  any  distance  at  which  it 
can  be  distinctly  defined.  Draw  on  the  board  a  semicircle  having  the  point 
a  for  its  centre  and  passing  through  the  pin,  and  plant  along  the  circle  a 
number  of  similar  pins,  at  an  angular  distance  from  each  other  of  5  degrees. 
If  the  eye  is  fixed  on  any  of  these  pins,  it  will  be  seen  that  its  next  neighbours 
only  are  seen  distinctly. 

(l))  Draw  two  parallel  lines  in  white,  on  a  black  ground,  each  J  millimetre 
wide,  and  separated  by  an  interval  of  the  same  width.  Place  the  board 
against  a  wall,  and  fix  one  eye  on  it  at  a  distance  of  five  feet  (li  metre,  and 
consequently  100  times  as  far  from  the  crossing  point  as  the  surface  of  the 
retina).  In  a  normal  eye  the  two  lines  can  be  distinguished  at  that  distance  : 
if  not,  lessen  the  distance  until  this  is  the  case.  If  the  eye  is  myopic,  a  cor- 
recting lens  must  be  used. 

In  those  of  the  following  experiments  which  depend  on  the  blending  of 
retinal  excitations  which  occurs  when  these  follow  each  other  in  rapid  succes- 
sion, a  circular  brass  plate  which  revolves  on  a  central  axis  is  used.  It  is 
furnished  with  an  arrangement  by  which  its  rate  of  revolution  at  any  desired 
moment  can  be  measured. 


136  VISION. 

6.  Duration  and  culmination  of  light  sensations.— On  a 

black  card  draw  two  concentric  circles,  of  which  the  respective  diameters  are 
6  and  10  inches.  Draw  a  straight  line  through  the  centre,  so  as  to  divide  the 
annular  space  between  them  into  two  equal  parts.  Cover  one  of  these  spaces 
with  white  paper.  Cut  out  the  card  along  the  outer  circle  and  fix  it  to  the 
revolving  disk. 

If  the  rate  of  revolution  is  gradually  increased,  the  moment  can  be  deter- 
mined at  which  the  sensations  due  to  successive  exposures  of  the  white 
sector  become  blended.  It  will  be  found  that  this  happens  when  the  rate 
of  revolution  is  such  that  the  white  is  visible  each  revolution  for  from  o""i5 
to  o"  '2  ;  for  the  time  required  for  the  light  given  off  by  a  white  surface  in 
common  daylight  to  produce  its  full  sensational  effect,  is  about  a  sixth  of  a 
second.  If  the  rate  of  revolution  is  further  increased,  the  subjective  lumi- 
nosity diminishes,  but  finally  becomes  constant.  Its  brightness  is  then  just 
half  of  that  of  the  white  paper  at  rest. 

7-  Diminution  of  sensational  effect  in  continued  exci- 
tation of  the  Retina. — To  prove  that  when  the  eye  is  exposed  to  the 
light  from  a  bright  surface,  the  apparent  luminousness  of  the  surface  after 
culminating  gradually  diminishes,  fix  against  a  wall  a  black  sheet  of  paper 
with  a  small  white  square  in  the  middle,  and  place  beside  it  a  white  sheet  of 
similar  size.  Having  fixed  the  eye  steadily  on  the  white  square,  suddenly 
direct  it  to  the  adjoining  white  surface.  A  grey  square  is  seen  on  a  white 
ground,  of  which  the  shade  differs  according  to  the  number  of  seconds  that  the 
white  square  has  been  contemplated. 

8.  Smallest  perceptible  difference.— Prepare  a  piece  of  black 

paper,  six  centimeters  in  length,  and  varying  in  width  from  2  millims.  to 
8  millims.  Cut  it  transversely  into  six  bits,  and  apply  the  smallest  to  a  white 
disk,  half  way  between  centre  and  circumference,  with  its  long  edge  against 
a  diameter  of  the  disk.  Set  the  disk  in  rapid  revolution  and  observe  the 
effect.  Replace  the  bit  of  black  paper  by  the  one  next  it  in  width,  and  repeat 
the  observation.  Proceed  in  this  way  until  a  faint  grey  ring  is  seen,  when  the 
disk  is  in  revolution.  This  happens  when  the  width  of  the  black  surface  is 
about  one  hundredth  of  the  circumference  of  the  ring. 

9.  Visual  perception  of  Motion. — When  a  disk  on  which  a  num- 
ber of  concentric  spirals  at  equal  distances  from  each  other  are  inscribed,  is 
contemplated  in  rapid  revolution,  radial  motion  is  perceived,  which  is  centri- 
petal or  centrifugal,  according  to  the  direction  of  rotation.  If  the  eye  is  sud- 
denly directed  to  a  blank  surface,  i-adial  motion  is  still  for  a  time  perceived, 
but  it  is  in  the  opposite  direction.  This  experiment  serves  not  only  to  illustrate 
the  principle  enunciated  on  p.  97,  but  to  prove  that  the  subjective  jjerception 
is  not  due,  as  has  been  supposed  in  other  similar  cases,  to  felt  motions  of  the 
eyeballs. 

P'or  experiments  relating  to  the  blending  of  sensations  of  colour  (p.  112), 
disks  are  used,  each  of  which  has  a  radial  cut  extending  from  the  circular  hole 
in  the  centre,  to  the  circumference.  Two  or  more  of  these  cardboard  disks 
can  be  fixed  to  the  brass  disk,  in  such  a  way  that  a  sector  of  each  colour  may 
be  exposed,  and  that  their  relative  areas  may  be  varied  at  will.  For  many 
purposes  of  study,  the  following  method  of  blending  is  more  useful : — 


VISION.  137 

Fix  a  pane  of  plate  glass  vertically  across  the  miiKlIe  of  a  board  about  16 
inches  long  by  8  wide.  On  either  side  place  a  sheet  of  paper  of  the  colours 
■which  it  is  desiretl  to  blend.  Arrange  the  board  so  that  the  illumination  of 
€ach  sheet  may  be  varied,  independently  of  that  of  the  other,  and  that  one 
sheet  is  seen  through  the  glass,  the  other  by  reflection. 

10.  The  angle  of  rotation  (>ee  p.  113). — Draw  on  a  wall  of  a  mode- 
rately dark  room,  a  horizontal  line,  at  a  height  of  a  couple  of  feet  above  that 
of  the  eyes.  In  a  black  card,  cut  out  a  cross,  each  bar  of  which  should  be 
about  a  twentieth  of  an  inch  in  width.  Close  one  eye,  and  place  the  cross 
between  the  other  and  a  bright  lamp,  and  fix  the  eye  on  the  luminous  cross  for 
several  seconds.  Then  turn  to  the  wall,  which  should  be  at  a  distance  of 
four  or  five  feet,  and  direct  the  eye  to  a  point  exactly  opposite  it  and  at  the 
same  level.  If  now  the  eye  is  fixed  on  a  point  in  the  horizontal  line  imme- 
diately above  the  first  (the  position  of  the  head  being  unaltered),  it  is  seen 
that  the  transverse  bar  of  the  bright  image  of  the  cross  coincides  with  the 
line.  But  if  (the  eye  remaining  fixed)  the  head  is  turned  to  the  right, 
the  image  gradually  assumes  an  appearance  of  distortion,  the  upper  end 
of  the  upright  bar  seeming  to  incline  to  the  left,  and  the  outer  end  of  the 
horizontal  bar  to  incline  upwards.  As  in  reality  the  horizontal  bar  coincides 
•with  the  horizontal  meridian  line  of  the  retina,  it  is  clear  that  the  retinal 
image  of  the  horizontal  line  crosses  the  meridian  line  at  an  acute  angle.  This 
angle  is  the  angle  of  rotation  for  the  particular  (tertiary)  position  assumed  by 
the  eye. 

!!•  Judgment  of  Form. — For  experiments  on  this  subject  pairs  of 
diagrams  representing  respectively  the  right  and  left  aspects  of  characteristic 
objects  are  used,  of  which  the  retinal  images  are  blended  by  means  of  the 
stereoscope.  The  most  important  obsers'ations  are  the  following  : — (a)  If  two 
diagrams  representing  the  right  and  left  aspects  of  a  pyramid  are  imaged  on 
the  right  and  left  retina,  and  the  images  blended  by  giving  the  eyes  the  degree 
of  convergence  necessary  to  unite  the  apices,  a  solid  pyramid  is  seen.  If  the 
diagrams  are  transposed  and  the  process  repeated  the  pyramid  appears 
hollow.  (/')  If  two  similar  diagrams  are  viewed  stereoscopically,  of  which  one 
is  represented  white  with  black  edges  on  a  black  ground,  and  the  other  black 
with  white  edges  on  a  white  ground,  the  combined  image  is  lustrous. 

12.  Judgment  of  Distance. — if  a  number  of  balls  of  similar  colour, 
but  differing  in  size,  are  allowed  to  fall  one  after  another  before  one  eye,  the 
the  other  being  closed,  at  such  distances  that  in  each  case  their  retinal  images 
are  equal,  and  at  such  velocities  that  their  images  pass  over  the  same  retinal 
distance  in  the  same  time,  the  observer  is  unable  to  form  any  judgment  either 
as  to  their  size,  distance,  or  rate  of  motion.  All  of  these  can  be  judged  of  at 
once  if  the  other  eye  is  opened.     For  this  experiment  an  apparatus  is  used. 


139 


DEMONSTRATIONS 
RELATING  TO  THE  FUNDAMENTAL  PHENOMENA 

OF 

CIRCULATION  AND  RESPIRATION, 

AND   TO   THE 

ELECTROMOTIVE     PROPERTIES    OF    MUSCLE. 


I. — Mode  of  Measuring  and  Rtxording  the  Arlcrial  Frtssun'.      Use 
of  Recording  Apparattts. 

The  instrument  used  is  called  a  kymograph  {see  p.  6i).  The  arterial 
cannula  is  a  T-shaped  tube  of  glass.  By  its  stem,  it  is  connected  with  the 
manometer  (a  U-shaped  glass  tube  containing  mercury).  One  branch  of  the 
T  is  drawn  out  and  bevelled  so  as  to  be  easily  introduced  into  the  artery  :  to 
the  other  is  fitted  a  short  piece  of  indiarubber  tubing,  guarded  by  a  steel  clip. 
The  stem  of  the  cannula  communicates  with  the  proximal  arm  of  the  mano- 
meter by  an  unyielding  tube  of  lead  or  guttapercha.  The  proximal  arm  {that 
connected  with  the  cannula)  also  communicates  by  a  long  flexible  tube  with  a 
bottle  containing  solution  of  bicarbonate  of  sodium  under  pressure.  The  mano- 
meter is  fixed  to  the  recording  apparatus,  so  that  its  oscillations  are  inscribed  on 
the  moving  surface.  This  is  effected  by  means  of  a  style  earned  by  a  vulcanite 
rod,  which  floats  on  the  surface  of  the  mercuiy  in  the  distal  (open)  limb  of  the 
manometer.  The  recording  cylinder  is  driven  by  clockwork  :  it  is  either 
covered  with  smoked  glazed  paper,  or  is  fed  by  an  endless  roll  of  paper,  in 
which  case  a  sable  pencil,  charged  with  coloured  ink,  is  substituted  for  the 
style.  The  paper  surface  in  either  case  moves  at  a  uniform,  rate  of  20  inches 
per  minute. 

The  artery  used  is  the  carotid  of  the  rabbit.  The  distal  end  of  the  prepared 
part  of  the  vessel  is  ligatured.  The  proximal  end  is  temporarily  closed  by  a 
spring-clip.  The  vessel  having  been  opened  near  the  ligature,  the  cannula 
is  introduced  and  secured  in  its  place  by  a  second  ligature,  its  drawn-out 
end  being  directed  towards  the  heart.  This  done,  the  guttapercha  tube  of 
the  manometer  is  connected  with  the  stem  of  the  cannula,  and  the  whole 
system  filled  with  solution  of  sodic  bicarbonate  under  a  pressure  of  about 
four  inches  of  mercur)'.  On  removing  the  clip  on  the  arter)',  communi- 
cation is  established  between  the  arterial  system  and  the  manometer, 
which  now  records  the  variations  of  arterial  pressure.  The  tracing  exhibits 
larger  (respiratory)  undulations,  on  each  of  which  many  smaller  undulations 
(cardiac  pulsations)  are  inscribed.     It  shows  (i)  that  each  contraction  of  the 


I40  DEMONSTRATIONS. 

left  ventricle  produces  a  momentary  increase  of  arterial  pressure  ;  (2)  tliat  the 
pressure  increases  after  each  inspiration,  and  sinks  in  the  interval ;  {3)  that 
during  the  rise  of  pressure,  the  pulsations  are  more  frequent  than  during  the 

fall.    Excitation  of  the  Cardiac  end  of  the  divided  Vagus, 

by  faradization,  produces  (if  weak  induction  currents  are  used)  diminution  of 
the  frequency  of  the  heart's  pulsation  and  of  the  arterial  pressure.  If  stronger 
currents  are  used,  the  heart  is  arrested  in  diastole  [see  p.  85). 

[N.B.  In  each  of  the  Demonstrations  I.,  II.,  III.,  and  IV.,  a  rabbit  is 
used,  which  is  rendered  completely  insensible  by  a  suitable  anaesthetic,  and  is 
killed  before  recover)-.] 


II. —  77ie  Normal  Respiratory  Movements.      Infltmue  of  the    Vagtis  Nerve 
and  of  its  Centre.     Apu^a  and  Dyspncea. 

The  motions  of  a  metal  plate  which  is  kept  in  constant  contact  with  the 
posterior  surface  of  the  central  tendon  of  the  diaphragm  of  the  rabbit,  by  the 
pressure  of  a  spring  are  communicated  by  a  long  steel  wire  to  the  vertical  arm 
of  a  bell-crank  lever.  The  horizontal  arm  of  the  lever  is  prolonged,  and  bears 
a  style  by  which  an  enlarged  record  of  the  respiratory  motion  of  the  diaphragm 
is  inscribed  on  the  cylinder  of  the  recording  apparatus.  The  rate  of  movement 
of  the  cylinder  is  the  same  as  in  the  last  demonstration. 

The  inspiratory  contraction  of  the  diaphragm  is  expressed  by  the  descent 
of  the  writing  style,  its  relaxation  by  the  ascent,  which  is  at  first  rapid,  but 
afterwards  more  gradual. 

Apnoea.  when  by  excessive  artificial  respiration  the  circulating  blood 
becomes  overcharged  with  oxygen,  all  respiratory  movement  ceases.  On 
discontinuing  the  injections  of  air,  the  respirations  after  a  time  begin  again  : 
at  first  they  are  scarcely  perceptible,  but  each  exceeds  its  predecessor  in 
extent,  until  the  normal  is  reached. 

Dyspnoea,  when  nitrogen  containing  an  inadequate  percentage  of 
oxygen  is  respired,  the  opposite  effect  to  that  described  above  is  produced. 
The  respirations  become  more  ample  and  more  frequent,  and  the  auxiliary 
muscles  are  brought  into  action.  No  such  effect  is  produced  by  an  atmosphere 
containing  as  much  as  ten  per  cent,  of  COj,  provided  that  the  supply  of 
oxygen  is  sufficient. 

Excitation  of  the  Superior  Laryngeal  Nerve.— Excitation 

of  the  central  end  of  the  trunk  of  the  superior  lar>'ngeal  nerve,  by  faradization, 
arrests  the  respiratory  movements,  the  diaphragm  becoming  stationary  in  the 
position  of  expiration.  When  extremely  feeble  currents  are  used,  rhythmical 
movements  may  continue  at  long  intervals.  Introduction  of  irritant  gases  or 
vapours  into  the  larj-nx  produces  similar  effects. 

Similar  excitation  of  the  central  end  of  the  divided  vagus,  below  the  cricoid 
cartilage,  produces  effects  which  differ  according  to  the  strength  of  the  induction 
currents  employed.  When  currents  of  moderate  strength  are  used,  the 
diaphragm  remains  during  the  excitation  in  the  position  of  inspiration,  the 
state  of  contraction  being,  however,  usually  interrupted  by  momentary  relaxa- 
tions at  short  intervals. 


DEMONSTRATIONS.  I4I 


III. — Infliuitce   of  the  Cardiac  and    Vasomotor    Centres  on   the    Circulation 
and  on  the  Motions  of  the  Heart. 

The  atlanto-occipital  membrane  having  been  previously  exposed,  the 
carotid  is  connected  with  the  kymograph.  A  record  is  taken,  and  the  mean 
arterial  pressure  measured.  On  faradization  of  the  spinal  cord,  at  the  level  of 
the  third  vertebra,  mixed  effects  are  observed,  due  partly  to  the  excitation  of 
the  vascular  nerves,  partly  to  escape  of  induction  currents  to  the  cardiac  centre. 
If  both  vagi  have  been  previously  divided,  those  due  to  the  latter  cause  do  not 
appear.  The  cord  is  now  severed  above  the  seat  of  excitation,  respiration 
being  continued  artificially  :  the  arterial  pressure  sinks  to  a  third  of  the  previous 
mean.  The  excitation  is  repeated  ;  the  pressure  rises  rapidly,  the  heart  beating 
with  great  frequency.  On  opening  the  thoracic  cavity,  the  action  of  the  heart 
may  be  studied.  It  is  seen  that  so  long  as  artificial  respiration  is  continued, 
it  beats  regularly.  If  the  injections  of  air  are  intermitted  for  a  few  moments,  its 
cavities  become  more  distended  and  its  action  more  vigorous  than  before,  and 
a  similar  effect  is  produced  by  excitation  of  the  spinal  cord. 


IV. — Functions  of  Vascular  Nerz'cs. 

Constricting  Nerves. — Division  of  the  trunk  of  the  sympathetic 
opposite  the  cricoid  cartilage  is  followed  by  dilatation  of  the  central  artery  of 
the  lobe  of  the  ear  on  the  same  side,  and  increase  of  vascularity.  On  compar- 
ing the  temperature  of  the  congested  lobe  with  that  of  the  other  side,  it  is  found 
to  be  two  or  three  degrees  higher.  The  pupil  of  the  same  side  is  more 
contracted  than  the  opposite  one.  Excitation  of  the  end  next  the  superior 
ganglion  produces  constriction  of  the  central  artery  and  abolishes  the  conges- 
tion of  the  lobe. 

Dilating  Nerves. — Excitation  of  the  central  end  of  the  great  auricular 
nerve  (or  of  the  posterior  auricular)  produces  temporary  vascular  changes, 
which  are  identical  with  those  permanently  produced  by  section  of  the  sympa- 
thetic. 

Depressor  Nerve. — Excitation  of  the  central  end  of  the  divided 
depressor  occasions  general  diminution  of  arterial  pressure  (dependent  on 
dilatation  of  the  blood-vessels  supplied  by  the  splanchnic  nerves).  If  the 
vagi  have  been  previously  divided,  the  diminution  of  pressure  is  not  asso- 
ciated with  any  change  in  the  frequency  of  the  contractions  of  the  heart. 


V. — Moz'ements  of  Circulation  and  Rcsfiration  in  Man. 

I.  The  Cardiograph  and  Sphygmograph.— a.  Two  receiving 

tympana  (cardiographs)  are  used.  One  is  applied  to  the  seat  of  the  cardiac 
impulse,  the  other  to  the  carotid  artery.  The  two  recording  tympana  with 
which  these  are  severally  connected,  inscribe  the  motion  of  the  heart  and  that 
of  the   artery  respectively,  on  the  same  cylinder.      The   arterial   expansion 


142  DEMONSTRATIONS. 

follows  that  of  the  heart  at  an  interval  of  about  eight-hundredths  of  a  second. 
The  duration  of  the  ventricular  impulse  is  about  three-tenths  of  a  second, 

b.  The  sphygrnograph  having  been  adjusted  so  as  to  record  the  radial  pulse, 
a  receiving  tympanum  on  the  carotid  is  connected  with  a  recording  tympanum 
attached  to  the  frame  of  the  sphygmograph,  so  that  its  lever  writes  on  the 
same  surface  as  that  of  the  sphygmograph.  The  interval  of  time  between  the 
impulse  of  the  carotid  and  that  of  the  radial  is  about  the  same  as  that  between 
the  carotid  and  the  heart. 

2.  Tlie  Stethograpll. — The  changes  of  form  of  the  thorax  in  respira- 
tion are  investigated  by  the  measui-ement  of  the  diameters  of  the  chest.  The 
most  important  diameters  are  the  antero-posterior  (from  upper  end  of  sternum 
to  third  dorsal  spine,  150  millims.  and. from  lower  end  of  sternum  to  eighth 
spine,  200  millims.);  the  transverse  (at  the  eighth  rib,  about  230  millims.). 
These  measurements  refer  to  an  adult  male,  as  taken  during  the  respiratory 
pause.  The  first  of  these  diameters  increases  about  a  millimeter,  the  second 
about  two  millimeters,  and  the  third  about  two  and  a  half  in  ordinary  tranquil 
inspiration.  These  measurements,  when  recorded  by  the  stethograph,  yield 
the  ' '  respiratory  curve. " 


\l.  —  The  Heart  of  the  Frog. 

1.  Rhythmical  Motions  of  the  Ventricle  ;    Influences 
thereon  of  Temperature  and  other  External  Conditions. 

2.  The  Cardiac  Vagus,  and  the  Intracardiac  Inhibitory- 
Centre. 

The  experiments  relating  to  these  subjects  are  described  in  the  Practical 
Exercises.     Such  of  them  only  as  can  be  seen  at  a  distance  are  shown. 


VII. — Electromotive  Phenomena  of  Muscle. 

The  most  important  instnament  used  is  a  Thomson's  Reflecting  Galvanometer 
of  high  resistance,  the  terminals  of  which  are  connected  by  insulated  copper 
wires  with  non-polarizable  electrodes.  These  are  in  contact  by  their  clay 
plugs  with  the  two  surfaces  to  be  compared. 

To  the  needle  of  the  galvanometer  a  light  concave  mirror  is  attached,  on 
which  a  beam  of  light  falls  and  is  focussed,  after  reflection,  on  a  divided 
screen.  Thus  the  smallest  deflection  of  the  needle  (by  which  any  electrical 
difference  between  the  two  contacts  is  indicated)  can  be  exactly  measured. 
By  means  of  a  suitable  shunt,  either  the  whole,  a  tenth,  or  other  decimal 
fraction  of  any  current  flowing  through  the  circuit  can  be  led  through  the 
galvanometer. 

I.  Electromotive  Phenomena  of  Muscle.— The  gastrocnemius 

muscle  of  the  frog  is  used.    One  of  the  electrodes  is  in  contact  with  the  convex 
surface  of  the  muscle  near  its  upper  end,  the  other  with  the  expansion  of  the 


DEMONSTRATIONS.  I43 

tenJo  Achillis.  In  this  arrangement  the  surface  of  the  tendon  is  negative  to 
that  of  the  muscle. 

2.  On  exciting  the  muscle  by  faradizing  its  nerve,  a  deflection  takes  place 
in  such  a  direction  as  to  indicate  that  the  electrical  difference  between  the 
two  surfaces  is  diminished.  After  excitation  the  needle  resumes  its  former 
position. 

3.  The  electrode  in  contact  with  the  tendinous  expansion  is  now  brought 
near  to  its  fellow,  so  that  both  contacts  are  now  muscular.  They  are  nearly 
isoelectricai.  On  injuring  the  lower  of  the  two  contacts  mechanically  or  by 
heat,  it  becomes  at  once  strongly  negative.  On  excitation  of  the  nerve  by 
induced  currents,  the  negativity  diminishes  as  before. 

4-  Electromotive  Phenomena  of  the  Ventricle  of  the 

Frog  Heart. — A  Stannius'  Heart  Preparation  (jcv  Practical  Exercises)  is 
"  led  oft""  by  contacts  at  its  apex  and  base.  If  the  heart  is  uninjured,  these 
surfaces  will  be  found  to  be  nearly  isoelectricai.  On  injuring  either  surface  it 
becomes  negative. 

2.  A  normally  contracting  heart  is  led  off  by  contacts  similarly  situated. 
Each  contraction  is  accompanied  by  a  deflection  of  the  needle,  indicating  that 
the  apex  becomes  first  positive  then  negative.  By  injuring  the  apex,  mechani- 
cally or  otherwise,  the  deflection  becomes  entirely  positive. 

3.  A  "ventricle  preparation"  is  led  off  at  apex  and  cut  surface.  During 
contraction,  the  effect  is  similar,  but  the  negative  deflection  is  much  larger. 

4.  A  ventricle  apex  preparation  (which  does  not  contract  spontaneously)  is 
led  off  as  above.  Its  cut  surface  is  at  first  strongly  negative  to  the  apex.  On 
excitation  at  the  base  by  a  single  induction  shock,  the  ventricle  contracts,  its 
contraction  being  accompanied  by  a  deflection  indicating  that  the  apex  becomes 
necative. 


H.  K.  Lewis,  Printer,  136  Gower  Street,  Lonton. 


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